Predicting wetland functions at the landscape level for coastal Georgia using NWIPLUS data

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Cover: Salt marsh on Little St. Simons Island (R. Tiner photograph).
Predicting Wetland Functions at the Landscape Level
for Coastal Georgia Using NWIPlus Data
Ralph W. Tiner
Regional Wetland Coordinator
U.S. Fish & Wildlife Service
Northeast Region
300 Westgate Center Drive
Hadley, MA 01035
Prepared In Cooperation With the
Georgia Department of Natural Resources
Coastal Resources Division, Brunswick, GA and
Atkins North America, Raleigh, NC
August 2011
This publication should be cited as:
Tiner, R.W. 2011. Predicting Wetland Functions at the Landscape Level for Coastal Georgia
Using NWIPlus Data. U.S. Fish and Wildlife Service, National Wetlands Inventory Program,
Region 5, Hadley, MA. In cooperation with the Georgia Department of Natural Resources,
Coastal Resources Division, Brunswick, GA and Atkins North America, Raleigh, NC. 29 pp.
Table of Contents
Page
Introduction 1
Creating the NWIPlus Database 4
Limitations of the Preliminary Wetland Functional Assessment 6
Rationale for Preliminary Functional Assessments 8
Surface Water Detention 9
Coastal Storm Surge Detention 10
Streamflow Maintenance 10
Nutrient Transformation 12
Carbon Sequestration 14
Retention of Sediment and Other Particulates 15
Bank and Shoreline Stabilization 16
Provision of Fish and Aquatic Invertebrate Habitat 16
Provision of Waterfowl and Waterbird Habitat 18
Provision of Other Wildlife Habitat 20
Provision of Habitat for Unique, Uncommon, or Highly Diverse
Plant Communities 22
Summary 23
Acknowledgments 24
References 25
This page is intentionally blank.
1
Introduction
The Georgia Department of Natural Resources (GA DNR) has recently updated National
Wetlands Inventory (NWI) data for the state’s six coastal counties. The U.S. Fish and Wildlife
Service (Service) has recognized the potential application of NWI data for watershed
assessments, but realized that other attributes would have to be added to the data to facilitate
functional analysis. In the early 1990s, Dr. Mark Brinson conceived a hydrogeomorphic
approach to wetland functional assessment that uses comparison of field-verified properties of
existing wetlands to those from a set of reference wetlands as a means of assessing a wetland’s
proximity to or departure from reference condition (Brinson 1993a). This approach provided the
impetus for the Service to develop other attributes to expand the NWI database and make it more
useful as a tool for landscape-level functional assessment of wetlands.
In the mid-1990s, the NWI developed a set of abiotic descriptors to describe a wetland's
landscape position, landform, water flow path, and waterbody type (LLWW descriptors; Tiner
1995, 1996a, b). Use of the initial set of keys for pilot watershed projects led to a refinement and
expansion of the keys in subsequent years (Tiner 1997a, b, 2000, 2002, 2003a). The expanded
NWI database is called NWIPlus because it significantly increases the amount of information
collected for mapped wetlands (Tiner 2010). These data allow for improved characterization of
wetlands across the landscape and make it possible to predict wetland functions at the landscape,
watershed, or regional scale. Numerous projects have created NWIPlus data and used the data to
better describe wetlands in watersheds or other specific geographic areas and produce
preliminary assessments of wetland functions (Table 1). In conducting these studies in the
Northeast, the Service worked with local and regional wetland experts to develop relationships
between wetland characteristics recorded in the database and wetland functions. The results
reflect our best approximation of what types of wetlands are likely to perform certain functions
at significant levels based on the characteristics in the NWIPlus database. Besides the Service’s
applications of these techniques, several states have been building NWIPlus or similar databases
or have plans to conduct at least a pilot study including Kansas, Michigan, Minnesota, Montana,
New Mexico, and Wisconsin (Tiner 2010). The State of Delaware has worked with the Service
to update NWI data and create a statewide NWIPlus database, and will use the information to
produce a series of reports on wetland status, recent and historic trends, wetland functions, and
potential wetland restoration sites.
2
Table 1. Areas where the Service created a NWIPlus database and where functions have been
analyzed or are planned for analysis. (* - functional assessment planned for 2011.)
State Project Area Approximate Area
(square miles)
Alaska Anchorage C7 quadrangle* 232
California Ventura River watershed 232
Connecticut entire state (planned)* 4,900
Delaware entire state* 1,900
Nanticoke watershed 490
Maine Casco Bay 1,216
Maryland Coastal Bays watershed 296
Nanticoke watershed 323
Massachusetts Boston Harbor and vicinity 232
Cape Cod and the Islands 665
Minnesota Fond du Lac reservation* 158
Mississippi Coastal zone* 1,450
New Jersey entire state* 7,500
Hackensack River watershed 197
New York Greater Buffalo area* 1,200
Catherine Creek watershed 100
Catskill watershed 571
Croton watershed 391
Cumberland Bay watershed 55
Delaware River watershed 1,013
Hackensack River watershed 197
Hudson River-Snook Kill watershed 254
Peconic River watershed 92
Post Creek-Sing Sing Creek watershed 59
Salmon River-So. Sandy Creek watershed 117
Sodus Creek watershed 54
Sodus Bay-Wolcott Creek watershed 65
Sucker Brook-Grass River watershed 124
Upper Tioughnioga River watershed 270
Upper Wappinger Creek watershed 136
Long Island* 1,400
Pennsylvania Delaware River and Lake Erie coastal zones 113
Rhode Island entire state* 1,100
South Carolina Horry and Jasper Counties* 3,100
Texas Corpus Christi area* 1,900
Vermont Southern part of state* 580
Wyoming Shirley Basin* 290
3
The State of Georgia recently added LLWW descriptors to their updated wetland inventory data
to create an NWIPlus database for six coastal counties. The NWIPlus data will be used to better
characterize wetlands in this region and to be able to predict wetland functions at the landscape
level. In order to do the latter, the relationships (formerly called correlations) developed for use
in the northeastern United States were introduced to and reviewed by a group of Georgia
scientists from federal, state, and local agencies, non-profit organizations, and academic
institutions at an August 31, 2010 workshop on Little St. Simons Island. The peer group
provided comments that were used to re-evaluate the relationships and tailor them to coastal
Georgia. In cases where there were differences in opinions, the points were considered and
decisions were made by consensus between the Coastal Resources Division of the Georgia
Department of Natural Resources, Atkins North America (formerly PBS&J Inc., Raleigh, NC),
and Ralph Tiner (U.S. Fish and Wildlife Service, Region 5, Hadley, MA).
The purpose of this report is to explain how the NWIPlus data could be and was used for
predicting wetland functions at the landscape-level for coastal Georgia and the rationale for
assigning certain biotic and/or abiotic characteristics to eleven wetland functions: 1) surface
water detention, 2) coastal storm surge detention, 3) streamflow maintenance, 4) nutrient
transformation, 5) carbon sequestration, 6) sediment and other particulate retention, 7) bank and
shoreline stabilization, 8) provision of fish and aquatic invertebrate habitat, 9) provision of
waterfowl and waterbird habitat, 10) provision of other wildlife habitat, and 11) provision of
habitat for unique, uncommon or highly diverse wetland plant communities.
4
Creating the NWIPlus Database
A set of abiotic attributes have been developed to increase the information contained in the NWI
database and to create a NWIPlus database. Four groups of attributes describe:
• landscape position (relationship of a wetland to a waterbody if present: marine—ocean,
estuarine—tidal brackish, lotic—river/stream, lentic—lake/reservoir, and terrene—not
significantly affected by such waters, or no waterbody present, or the source of a stream);
• landform (physical shape of the wetland—basin, flat, floodplain, fringe, island, and
slope);
• water flow path (inflow, outflow, throughflow, isolated, bidirectional-nontidal, and
bidirectional-tidal); and
• waterbody type (different types of estuaries, rivers, lakes, and ponds).
Collectively, they are known as LLWW descriptors, which represent the first letter of each
descriptor (landscape position, landform, water flow path, and waterbody type). Dichotomous
keys have been developed to interpret these attributes (Tiner 2003b; they will be amended in
2011 to reflect results of recent applications). Other modifiers are also included in these keys to
further describe wetland characteristics. LLWW descriptors are added to the NWI database by
interpreting topography from digital raster graphics (DRGs) or digital elevation model data
(DEMs), stream courses from the National Hydrography Dataset (NHD) and/or aerial imagery,
and waterbody types from aerial imagery (Figure 1). The interpretations are done by employing
some automated GIS-routines coupled with manual review and interpretation by wetland
specialists. This effort now increases the NWI workload by less than 10 percent.
The NWIPlus database adds value and increases the functionality of the original NWI database.
Besides providing more features that can be used to predict wetland functions from the NWI
database, NWIPlus makes it possible to better characterize the nation’s wetlands. For example,
all the palustrine wetlands, which account for 95 percent of the wetlands in the conterminous
United States, can now be linked to rivers, streams, lakes, and ponds where appropriate, so that
the acreage of floodplain wetlands, lakeside wetlands, and geographically isolated wetlands can
be reported. The Wetlands Subcommittee of the Federal Geographic Data Committee (FGDC)
recognized the value added by the LLWW descriptors and recommended that they be included in
wetland mapping to increase the functionality of wetland inventory databases (FGDC Wetlands
Subcommittee 2009).
5
Figure 1. Examples of application of LLWW descriptors to nontidal wetlands. Coding:
Landscape position = LE – Lentic, TE – Terrene, LR – Lotic River, LS – Lotic Stream;
Landform = BA – Basin, FP – Floodplain, FR – Fringe, SL – Slope; Water Flow Path = BI –
Bidirectional-nontidal, IS – Isolated, OU – Outflow, TH – Throughflow; Other descriptors: PD –
Pond, LK – Lake, hw – headwater, and pd – pond-bordering wetland. Note: If desired, ponds
and lakes can be further classified with landscape position resulting in codes of TEPDIS for the
isolated ponds and LSLKTH for the lake shown in this figure.
6
Limitations of the Preliminary Wetland Functional Assessment
Source data are a primary limiting factor for landscape-level functional assessment. NWI digital
data and existing stream data (e.g., National Hydrography Dataset) are used as the foundation for
these assessments. All wetland and stream mapping has limitations due to scale, photo quality,
date of the survey, and the difficulty of photointerpreting certain wetland types (especially
evergreen forested wetlands and drier-end wetlands; see Tiner 1997c, 1999 for details) and
narrow or intermittent streams especially those flowing through dense evergreen forests and
beneath built-up lands.
Recognizing source data limitations, it is equally important to understand that this type of
functional assessment is a preliminary one based on wetland characteristics interpreted through
remote sensing and using the best professional judgment of various specialists to develop
relationships between wetland characteristics in the database and wetland functions. It is
designed for landscape- or watershed-level assessments covering large geographic areas.
Wetlands are rated based on their biotic or abiotic characteristics as having high or moderate
potential for supporting a wetland function. Wetlands not assigned a rating are assumed to have
little or no potential for providing such function at a significant level. The ratings are based on a
review of the literature and best professional judgment by numerous scientists studying wetlands
from public agencies, private non-government organizations, and academia. Also, no attempt is
made to produce a more qualitative ranking for each function (comparing to a “reference” type
representing a wetland of the type in the ���best” condition, or on size or the degree to which it
actually performs a function given opportunity and adjacent land uses) or for each wetland based
on multiple functions as this would require more input from others and more data, well beyond
the scope of this type of broad-scale evaluation. For a technical review of wetland functions, see
Mitsch and Gosselink (2007) and for a broad overview, see Tiner (2005a).
Functional assessment of wetlands can involve many parameters. Typically such assessments
have been done in the field on a case-by-case basis, considering observed features relative to
those required to perform certain functions or by actual measurement of performance. The
preliminary assessments based on remotely sensed information do not seek to replace the need
for field evaluations since they represent the ultimate assessment of the functions for individual
wetlands. Yet, for a watershed analysis, basin-wide field-derived assessments are not practical,
cost-effective, or even possible given access considerations. For watershed planning purposes, a
more generalized assessment (level 1 assessment) is worthwhile for targeting wetlands that may
provide certain functions, especially for those functions dependent on landscape position,
landform, hydrologic processes, and vegetative life form (Brooks et al. 2004). Subsequently,
these results can be field-verified when it comes to actually evaluating particular wetlands for
acquisition purposes (e.g., for conserving biodiversity or for preserving flood storage capacity)
or for project impact assessment. Current aerial photography may also be examined to aid in
further evaluations (e.g., condition of wetland/stream buffers or adjacent land use) that can
supplement the preliminary assessment.
The landscape-level functional assessment approach -"Watershed-based Preliminary Assessment
of Wetland Functions" (W-PAWF) - applies general knowledge about wetlands and their
functions to develop a watershed overview that highlights possible wetlands of significance in
terms of performance of various functions. To accomplish this objective, the relationships
7
between wetlands and various functions are simplified into a set of practical criteria or
observable characteristics. Such assessments may be further expanded to consider the condition
of the associated waterbody and the neighboring upland or to evaluate the opportunity a wetland
has to perform a particular function or service to society, for example.
W-PAWF does not account for the opportunity that a wetland has to provide a function resulting
from a certain land-use practice upstream or the presence of certain structures or land-uses
downstream. For example, two wetlands of equal size and like vegetation may be in the right
landscape position to retain sediments. One, however, may be downstream of a land-clearing
operation that has generated considerable suspended sediments in the water column, while the
other is downstream from an undisturbed forest. The former should be actively performing
sediment trapping in a major way, whereas the latter is not. Yet if land-clearing takes place in
the latter area, the second wetland will likely trap sediments as well as the first wetland. The
entire analysis typically tends to ignore opportunity since such opportunity may have occurred in
the past or may occur in the future and the wetland is there to perform this service at higher
levels when necessary.
W-PAWF also does not consider the condition of the adjacent upland (e.g., level of disturbance)
or the actual water quality of the associated waterbody that may be regarded as important metrics
for assessing the health of individual wetlands. Collection and analysis of these data may be
done as a follow-up investigation, where desired.
It is important to re-emphasize that the preliminary assessment does not obviate the need for
more detailed assessments of the various functions and assessment of wetland condition and
opportunities to provide more benefits given the state of the contributing watershed and adjacent
land use activities. This preliminary assessment should be viewed as a starting point for more
rigorous assessments, since it attempts to cull out wetlands that may likely provide significant
functions based on generally accepted principles and the source information used for this
analysis. This assessment is most useful for regional or watershed planning purposes, for a
cursory screening of sites for acquisition, and to aid in developing landscape-level wetland
conservation and protection strategies. It can also be used to evaluate cumulative impacts on
wetlands on key functions as was done for the Nanticoke River watershed on the Delmarva
Peninsula (Tiner 2005b) or to consider the national and regional-scale impacts of policy changes
on certain wetland types (e.g., geographically isolated wetlands or headwater wetlands, or
determining significant nexus to waters of the United States). For site-specific evaluations,
additional work will be required, especially field verification and collection of site-specific data
for potential functions (e.g., following the hydrogeomorphic assessment approach as described
by Brinson 1993a or other onsite evaluation procedures, e.g., rapid field assessment). This is
particularly true for assessments of fish and wildlife habitats and biodiversity. Other sources of
data may exist to help refine some of the findings of this report (e.g., state natural heritage data).
Additional modeling could be done, for example, to identify habitats of likely significance to
individual species of animals based on their specific life history requirements (see U.S. Fish and
Wildlife Service 2003 for Gulf of Maine habitat analysis).
Also note that the criteria used for the relationships were based on Georgia’s application of the
Service's wetland classification (Cowardin et al. 1979). Regional applications of this system
may differ slightly depending on regional priorities, level of field effort, and knowledge of
wetland ecology. Use of the relationships in other regions of the country therefore may require
some adjustment based on these considerations.
8
Through this analysis, numerous wetlands are predicted to perform a given function at a
significant level presumably important to a watershed's ability to provide that function.
"Significance" is a relative term and is used in this analysis to identify wetlands that are likely to
perform a given function at a high or moderate level. It is also emphasized that the assessment is
limited to wetlands (i.e., areas classified as wetlands on NWI maps). Deepwater habitats and
streams were not included in the assessment, although their inherent value to wetlands and many
wetland-dependent organisms is apparent.
Rationale for Preliminary Functional Assessments
The W-PAWF approach (“watershed-based preliminary assessment of wetland functions”) is
intended to produce a more expansive characterization of wetlands and their likely functions and
data that can be used to help rank wetlands for acquisition, protection, or other purposes.
Presently, a maximum of eleven functions may be evaluated: 1) surface water detention, 2)
coastal storm surge detention, 3) streamflow maintenance, 4) nutrient transformation, 5) carbon
sequestration, 6) sediment and other particulate retention, 7) bank and shoreline stabilization, 8)
provision of fish and aquatic invertebrate habitat, 9) provision of waterfowl and waterbird
habitat, 10) provision of other wildlife habitat, and 11) provision of habitat for unique,
uncommon, or highly diverse wetland plant communities. The criteria used for identifying
wetlands of significance for each of these functions using Georgia’s NWIPlus database are
discussed below. The criteria and ratings were initially developed for northeastern wetlands by
the author of this report based on his knowledge of wetland characteristics and functions. The
draft criteria were then reviewed and modified for various watersheds based on comments from
wetland specialists working on specific watersheds in four Northeast states (Maine, New York,
Delaware, and Maryland). While many of the criteria are universally applicable, when applying
NWIPlus data to other regions for landscape-level functional assessment, the criteria and ratings
should be reviewed. For coastal Georgia, a workshop sponsored by the Georgia Department of
Natural Resources was conducted on August 31, 2010 to get input from local experts on the
applicability of these relationships for tidal and nontidal wetlands in six coastal counties (see
Acknowledgments for participants). The actual application of the Cowardin et al. (1979)
classification also needed to be considered as there may be differences in the level of
classification for individual projects, such as the use of water regime indicators that could affect
functional ratings.
In developing a protocol for designating wetlands of potential significance, wetland size was
generally disregarded from the criteria, with few exceptions (i.e., other wildlife habitat and
biodiversity functions). This approach was followed because it was felt that individual agencies
and organizations using the digital database and charged with setting priorities should make the
decision on appropriate size criteria as a means of limiting the number of priority wetlands as
necessary. There is no science-based size limit to establish significance for any function.
However, it is obvious that, all things being equal, a larger wetland will have a higher capacity to
perform a given function than a smaller one of the same type, although it is recognized that
certain wildlife species (e.g., amphibians) require a multitude of small wetlands to maintain their
local populations given vagaries of weather and its effect on habitat suitability.
9
After discussing a particular function and the wetland types that are likely to perform that
function, a list of wetland types is given for two levels of function. These types were determined
to have the potential to perform the subject function at a significant level.
ATTENTION: The types that are underlined are types that were actually mapped during the
inventory and will be displayed on the wetland function maps for coastal Georgia. The other
types (not underlined) are other wetlands that may perform that function at the specified level,
however no wetlands were classified as these types during this survey.
Surface Water Detention
This function is important for reducing downstream flooding and lowering flood heights, both of
which aid in minimizing property damage and personal injury from such events. In a landmark
study on the relationships between wetlands and flooding at the watershed scale, Novitzki (1979)
found that watersheds with 40 percent coverage by lakes and wetlands had significantly reduced
flood flows -- lowered by as much as 80 percent -- compared to similar watersheds with no or
few lakes and wetlands in Wisconsin. The same principles apply to Georgia where studies have
shown that watersheds with an abundance of wetlands moderate flood flows more than those
with less wetland (Wharton 1970). After heavy rains, the former watersheds take longer to reach
peak water levels and have less fluctuation than the latter watersheds which reach their peaks
more quickly, produce higher peaks, and tend to have more swift flows.
For purposes of landscape-level functional assessment following W-PAWF, this function will be
restricted to surface water storage of nontidal waters. Floodplain wetlands and other lotic
wetlands (basin and flat types) provide this function at significant levels. While tidal wetlands
along rivers serve at times to attenuate freshwater flood flows from upstream watersheds, they are
excluded from this function because they are subjected to frequent tidal flooding. The water
storage function of tidal wetlands for detaining storm surges is evaluated separately via the coastal
storm surge detention function. Stormwater detention ponds are designed for temporary storage of
surface water and are recognized as having a high level of performance for this function.
Wetlands dominated by trees and/or dense stands of shrubs could be deemed to provide a higher
level of this function than emergent wetlands, since woody vegetation (with higher frictional
resistance) may further aid in flood desynchronization. However, emergent wetlands along
waterways provide significant flood storage, so no distinction is made regarding the type of
vegetative cover. Floodplain width could also be an important factor in evaluating the
significance of performance of this function by individual wetlands (e.g., for acquisition or
strengthened protection), but there is no scientifically based criterion for establishing a
significance threshold based on size. Drier-end wetlands (e.g., flats), and isolated basins are
rated as having moderate potential.
For this function, the following relationships are used:
High Lentic Basin, Lentic Fringe, Lentic Island (basin and fringe),
Lentic Flat associated with reservoirs and flood control dams,
Lotic Stream Basin, Lotic Floodplain-basin, Lotic River Fringe,
Lotic Stream Fringe (not “A” water regime), Lotic River Island-basin,
Ponds Throughflow (in-stream) and associated Fringe and
Basin wetlands, Terrene Throughflow Basin, Stormwater
Treatment Ponds
10
Moderate Lotic River Floodplain-flat, Lotic River Fringe (other than above),
Lotic Stream Fringe (other than above), Lotic Stream Flat, Lotic
River Island-flat, Lentic Flat, Other Terrene Basins, Other Ponds
and associated wetlands (excluding sewage treatment ponds and
isolated impoundments), Terrene wetland associated with ponds
(TE__pd__, excluding isolated diked ponds), Terrene Flat
Note: Exclude the following: 1) artificially flooded wetlands (“K” water regime,
unless they are in a reservoir or dammed lake), 2) isolated impounded ponds and
associated wetlands, 3) any freshwater tidal wetlands that are in the Lotic
landscape position, and 4) any seasonally saturated wetlands (“B” water regime)
from this function.
Coastal Storm Surge Detention
This function is listed separately from Surface Water Detention to highlight the importance of
tidal wetlands and adjacent lowland wetlands at storing tidal waters brought into estuaries by
storms (e.g., tropical storms and hurricanes). Estuarine and freshwater tidal wetlands are
important areas for temporary storage of this water. Some nontidal wetlands contiguous to these
wetlands (e.g., low-lying terrene outflow basins - flatwoods) may also provide this function, but
do so only during the most extreme storm events, so they were rated as moderate for this
function. Note that tidal wetlands along rivers may also be important for attenuating freshwater
floodwaters resulting from heavy precipitation events upstream in the watershed.
For this function, the following relationships are used:
High Estuarine Basin, Estuarine Fringe, Estuarine Island, Lotic Tidal
Fringe, Lotic Tidal Island, Lotic Tidal Floodplain, Marine Fringe,
Marine Island
Moderate Other tidal wetlands not included above plus any Terrene wetland
(excluding SL – slope wetland) with “ed” modifier (nontidal
wetlands contiguous with estuarine wetlands discharging and likely
subject to infrequent or occasional flooding by storm tides) or with
“ow” modifier (overwash)
Streamflow Maintenance
There are four main sources of water to support stream flow: 1) groundwater, 2) interflow
through the soil, 3) precipitation, and 4) surface water runoff. Groundwater provides water for
base flows. Many wetlands are sources of groundwater discharge and those located in headwater
positions either the source of streams or along low-order perennial streams contribute
significantly to sustain streamflow in the watershed. Such wetlands are critically important for
supporting aquatic life in streams. The importance of maintaining natural streamflow patterns is
important to riparian vegetation as well as to resident aquatic species and altering those patterns
can negatively impact local biodiversity (Cowell and Stoudt 2002).
11
All wetlands classified as headwater wetlands are important for streamflow. Terrene headwater
wetlands, by definition, are sources of streams. They contribute groundwater (base flow) from
local unconfined aquifers and regional confined aquifers to support streamflow (Priest 2004).
Other headwater wetlands include lotic wetlands along 1st-order streams and lentic wetlands
associated with outflow lakes. Wetlands along 2nd-order streams in mountainous areas may be
classified as headwater wetlands as they probably are sites of groundwater discharge, but these
conditions do not apply to the Georgia coastal region since Georgia’s mountains are much
further inland. Ditched headwater wetlands are rated as moderate, since this alteration typically
results in faster release of water, thereby reducing the period of outflow. Outflow from
groundwater-fed wetlands (lacking a stream) may discharge directly into streams and thereby
contribute variable quantities of water for sustaining baseflows. These wetlands were rated as
moderate for this function. Lakes may also be important regulators of streamflow, so lentic
wetlands may be designated as significant to streamflow, with those in headwater positions being
rated high and others as moderate.
Floodplain wetlands are known to store water in the form of bank storage, later releasing this
water to maintain baseflows (Whiting 1998). Among several key factors affecting bank storage
are porosity and permeability of the bank material, the width of the floodplain, and the hydraulic
gradient (steepness of the water table). It is recognized that the wider the floodplain, the more
bank storage given the same soils. Gravel floodplains drain in days, sandy floodplains in a few
weeks to a few years, silty floodplains in years, and clayey floodplains in decades. In good
water years, wide sandy floodplains may help maintain baseflows. Bank stratigraphy is another
factor that could be considered important for streamflow maintenance (Christopher Cirmo, pers.
comm. 2006). For example, the presence of a “sand” layer between clay layers (such as in a
system where there have been historical floods) may affect the transmissivity of the bank. Bank
storage may serve to maintain streamflow in some fringe or floodplain wetlands, however a
rudimentary knowledge of the surficial stratigraphy is not normally available based solely on
remote data interpretation. Despite the variability in floodplain properties, the W-PAWF
assessment treats all nontidal floodplain wetlands and stream basins as having potential to
support streamflow, since remote sensing data does not include soil examinations or bank
stratigraphy and there is no recognized floodplain width designated to separate high from
moderate potential.
While diked ponds may contribute to streamflow when water overflows spillways or exceeds
height of water-control structures, these ponds typically reduce streamflow (McMurray 2007,
Van Liew 2004). However, some ponds may extend storm-flow over longer durations by
reducing peak flows (Bosch et al. 2003). Since impounded ponds are artificially created waters
that substantially alter natural streamflow characteristics they are not included as significant for
streamflow maintenance.
For this function, the following relationships are used:
High Unaltered Headwater Wetlands and Headwater Ponds (latter are
natural ponds not created or altered)
12
Moderate Ditched or excavated Headwater Wetlands (not impounded), Lotic
River (nontidal) Floodplain (excluding impounded or ditched),
Lotic Stream (nontidal) Basin (excluding impounded or ditched),
Terrene Basin Outflow wetlands (associated with streams not
major rivers; excluding impounded or ditched)
Note: Diked wetlands and ponds and excavated ponds should be excluded from this function.
Special Note: All wetlands important for streamflow maintenance should be considered to also
be important for fish and aquatic invertebrates as they are vital to sustaining streamflow
necessary for the survival of these aquatic organisms.
Nutrient Transformation
All wetlands recycle nutrients, but those having a fluctuating water table and corresponding
changes from aerobic to anaerobic conditions are best able to recycle nitrogen and other
nutrients. While vegetation slows the flow of water causing deposition of mineral and organic
particles with adsorbed nutrients (nitrogen and phosphorus), hydric soils are the places where
chemical transformations occur (Carter 1996). Microbial action in the soil is the driving force
behind chemical transformations in wetlands. Microbes need a food source to survive and
reproduce and in wetlands organic matter provides this needed sustenance. Wetlands with high
amounts of organic matter should have an abundance of microflora to perform the nutrient
cycling function. Wetlands are so effective at filtering and transforming nutrients that artificial
wetlands are constructed for water quality renovation (e.g., Hammer 1992). Natural wetlands
performing this function help improve local water quality of streams and other watercourses.
Oyster reefs are also recognized as important components for nitrogen cycling in estuaries
(Dame et al. 1985, Dame and Libes 1993, Fulford et al. 2010).
Numerous studies have demonstrated the importance of wetlands in denitrification. Simmons et
al. (1992) found high nitrate removal (greater than 80%) from groundwater during both the
growing season and dormant season in Rhode Island streamside (lotic) wetlands. Groundwater
temperatures throughout the dormant season were between 6.5 and 8.0 degrees C, so microbial
activity was not limited by temperature. Even the nearby upland, especially transitional areas
with somewhat poorly drained soils, experienced an increase in nitrogen removal during the
dormant season. This was attributed to a seasonal rise in the water table that exposed the upper
portion of the groundwater to soil with more organic matter (nearer the ground surface), thereby
supporting microbial activity and denitrification. Riparian forests dominated by wetlands have a
greater proportion of groundwater (with nitrate) moving within the biologically active zone of
the soil that makes nitrate available for uptake by plants and microbes (Nelson et al. 1995).
Riparian forests on well-drained soils are much less effective at removing nitrate. In a Rhode
Island study, Nelson et al. (1995) found that November had the highest nitrate removal rate due
to the highest water tables in the poorly drained soils, while June experienced the lowest removal
rate when the deepest water table levels occurred. Similar results can be expected to occur
elsewhere. For bottomland hardwood wetlands, DeLaune et al. (1996) reported decreases in
nitrate from 59-82 percent after 40 days of flooding wetland soil cores taken from the Cache
River floodplain in Arkansas. Moreover, they surmised that denitrification in these soils
appeared to be carbon-limited: increased denitrification took place in soils with more organic
matter in the surface layer. Nitrogen removal rates for freshwater wetlands are very high
(averaging from 20-80 grams/square meter) (Bowden 1987).
13
Nitrogen fixation has been attributed to blue-green algae in the photic zone at the soil-water
interface and to heterotrophic bacteria associated with plant roots (Buresh et al. 1980). In
working with rice, Matsuguchi (1979) believed that the significance of heterotrophic fixation in
the soil layer beyond the roots has been underrated and presented data showing that such zones
were the most important sites for nitrogen fixation in a Japanese rice field. This conclusion was
further supported by Wada et al. (1978). Higher fixation rates have been found in the
rhizosphere of wetland plants than in dryland plants. Nitrogen fixation converts atmospheric
nitrogen to a usable form for plants and helps enrich soils. Plants with the ability to fix nitrogen
(e.g., with symbiotic bacteria on root nodules) can thereby grow in otherwise inhospitable
nutrient-poor soils.
From the water quality standpoint, wetlands associated with watercourses are probably the most
noteworthy. Numerous studies have found that forested wetlands along rivers and streams
(Ariparian forested wetlands@) are important for nutrient retention and sedimentation during
floods (Whigham et al. 1988; Yarbro et al. 1984; Simpson et al. 1983; Peterjohn and Correll
1982). This function by forested riparian wetlands is especially important in agricultural areas.
Brinson (1993b) suggested that riparian wetlands along low-order streams may be more
important for nutrient retention than those along higher order streams.
Most of the groundwater flux from uplands to surface waters occurs in the non-growing season
in the Northeast and reasonable denitrification rates occur in spring and fall making sites that are
wet during these times important for nutrient retention (Art Gold, pers. comm. 2003). Wetlands
with seasonally flooded and wetter water regimes (including tidal regimes - seasonally flooded-tidal,
irregularly flooded, and regularly flooded) are identified as having potential to recycle
nutrients at high levels of performance. The soils of these wetlands should have substantial
amounts of organic matter near the surface to promote microbial activity and denitrification
when wet. Based on field observations, in general, there is a positive correlation between the
amount of organic matter and the degree of wetness as reflected by the NWI's water regime
classification in wetlands of the Nanticoke River watershed in Delaware (Amy Jacobs, pers.
comm. 2003). Periodically flooded soils also retain sediments and their adsorbed nutrients.
Drier-end wetlands -- those with a temporarily flooded water regime (including temporarily
flooded-tidal) and others with a seasonally saturated water regime -- are considered as having
moderate potential for performing this function, since they are relatively dry for most of the year.
For this function, relationships are the following:
High Vegetated wetlands (and mixes with nonvegetated wetlands or
unconsolidated bottom; only where vegetated predominates) with
seasonally flooded (C), semipermanently flooded (F),
semipermanently flooded-tidal (T), seasonally flooded-tidal (R),
irregularly flooded (P), regularly flooded (N), and permanently
flooded (H or L) water regimes, estuarine intertidal oyster reefs,
Vegetated wetlands with a permanently saturated water regime
Moderate Vegetated wetlands with seasonally saturated (B on the coastal
plain), temporarily flooded (A) or temporarily flooded-tidal (S)
14
water regimes; nonvegetated/vegetated wetlands (where
nonvegetated predominates) with seasonally flooded (C),
semipermanently flooded (F), semipermanently flooded-tidal (T),
seasonally flooded-tidal (R), irregularly flooded (P), regularly
flooded (N), and permanently flooded (H or L) water regimes
Carbon Sequestration
Concern over rising global temperatures and climate change has directed attention to wetlands
since they are recognized as important carbon sinks. Drainage of wetlands releases carbon to the
atmosphere in the form of carbon dioxide, one of several greenhouse gases influencing global
temperatures. In wetlands, organic matter (carbon) accumulates in the soils as well as in
vegetation. Woody plants, thereby, store carbon for longer periods than annual herbaceous
plants. While the above-ground biomass of perennial herbs is released back into the aquatic
ecosystem seasonally, the below-ground biomass remains in the substrate and contributes to
longer-term storage. Temperate and subtropical wetlands are recognized as important for
attenuating global warming (Whiting and Chanton 2001).
Interestingly, tidal salt marshes sequester up to fifty times more carbon per acre than is
sequestered by tropical forests (Pidgeon 2009). Salt marshes, unlike freshwater wetlands, do not
release significant quantities of methane (a recognized greenhouse gas contributing to global
warming) to the atmosphere (Chmura 2009). Studies in Georgia have found that among tidal
wetlands, the tidal freshwater wetlands and brackish marshes sequester more carbon and retain
more nutrients than salt marshes (Loomis and Craft 2010). In fact, tidal fresh and brackish
marshes sequestered 66 percent of the carbon and 69 percent of the nitrogen stored in all tidal
wetlands in the three-river system studied (Ogeechee, Altamaha, and Satilla) even though they
represent only 41 percent of the marsh area. Anaerobic conditions resulting from prolonged
flooding or soil saturation typically lead to an accumulation of organic matter. Therefore,
wetlands that experience longer duration of soil saturation should accumulate more organic
matter. Northern bogs that are nearly continuous saturated in boreal to arctic climates where low
evapotranspiration rates occur are recognized as major global carbon sinks. Consequently,
wetlands with the wetter water regimes (i.e., seasonally flooded and wetter) should store more
carbon than wetlands in the same region with drier water regimes that promote more oxidation
and decomposition of organic matter. Seasonally flooded and wetter vegetated wetlands are
rated as high for the carbon sequestration function, while drier wetlands (temporarily flooded
and seasonally saturated) are assigned a moderate rating. Tidal flats (unconsolidated shores,
mudflats in particular, except sandy beaches and sand flats) are listed as moderate because they
sequester carbon at lower rates than vegetated coastal wetlands (Duarte et al. 2005). Ponds were
also designated as moderate because recent studies have indicated the cumulative importance of
small ponds in sequestering carbon through sedimentation processes (Downing 2010). Several
types of ponds that are not likely to be capture organic-enriched sediment from local watersheds
are excluded from this function: aquaculture, commercial, industrial, residential-stormwater,
sewage treatment, and isolated diked ponds (impoundments).
High Tidal vegetated wetlands (including mixed with unconsolidated
shore), Nontidal vegetated wetlands that are seasonally flooded,
semipermanently flooded, or intermitttently exposed, Nontidal
vegetated wetlands that are permanently saturated
15
Moderate Nontidal vegetated wetlands that are temporarily flooded or
seasonally saturated, Tidal unconsolidated shore wetlands
(including mixes with vegetated types; focus on mudflats and
organic substrates for purely nonvegetated types; exclude sandy
beaches, sand flats, and flats with other substrates), Nontidal
nonvegetated/vegetated wetlands, Ponds (excluding aquaculture,
commercial, industrial, residential-stormwater, and sewage
treatment ponds plus isolated impoundments)
Retention of Sediment and Other Particulates
Many wetlands owe their existence to being located in areas of sediment deposition. This is
especially true for floodplain and estuarine wetlands. This function supports water quality
maintenance by capturing sediments with bonded nutrients or heavy metals as in and
downstream of urban areas (e.g., Gambrell 1994). Estuarine and floodplain wetlands plus lotic
(streamside) and lentic (lakeshore) fringe and basin wetlands including lotic (in-stream) ponds
are likely to trap and retain sediments and particulates at significant levels. Terrene throughflow
basins should function similarly. Vegetated wetlands will likely favor sedimentation over
nonvegetated wetlands and therefore they received a high rating versus moderate for the
nonvegetated types. Lotic flat wetlands are flooded only for brief periods and less frequently
than the wetlands listed above due to their elevation; they are classified as having moderate
potential for sediment retention. Throughflow (in-stream) ponds and associated fringe and basin
vegetated wetlands are rated as high, since they occur within the stream network where they trap
water-borne sediments. Stormwater treatment ponds are designed specifically to perform this
function, so they are rated as high. Other ponds and terrene basins may be locally significant in
retaining such materials, and are therefore designated as moderate. However, commercial,
industrial, residential, sewage treatment, golf, and mining ponds were not rated as significant
since many are isolated diked impoundments. Terrene flats are not rated as potentially
significant because they are level landscapes that do not appear to trap substantial amounts of
sediment from surrounding areas.
For this function, the following relationships are used:
High Estuarine vegetated (not floating mats), Lentic vegetated (not Flat
and not floating mats), Lotic vegetated (not Flat, not Floodplain-flat,
and not floating mats), Throughflow Ponds and Lakes (in-stream;
designated as PUB... on NWI) and associated vegetated
wetlands, Bidirectional-tidal Ponds and associated vegetated
wetlands, Terrene Throughflow Basin, Stormwater Treatment
Ponds
Moderate Estuarine nonvegetated (excluding rocky shore), Lotic
nonvegetated, Lotic Flat, Lotic Floodplain-flat, Lentic Flat, Marine
Fringe (excluding rocky shore), Marine Island (excluding rocky
shore), Other Terrene Basins, Terrene wetlands associated with
ponds (excluding some types of ponds - commercial,
industrial, sewage treatment, and mining), Other Ponds and Lakes
(classified as PUB... on NWI) and associated wetlands (excluding
16
some types of ponds – commercial, industrial, sewage treatment,
and mining and slope wetlands)
Bank and Shoreline Stabilization
Vegetation colonizing banks and shorelines stabilizes the soil or substrate and diminishes wave
action, thereby reducing shoreline erosion potential and increasing bank stability. Vegetated
wetlands along all flowing or large standing waterbodies (e.g., estuaries, lakes, rivers, and
streams) therefore provide this function at high levels. Intertidal oyster reefs when located along
shorelines help protect the shorelines from erosion and are therefore rated as high. Vegetated
wetlands along ponds are designated as moderate for this function since there is less wave or
erosive action along these shores. Since island wetlands are surrounded by water, they are not
considered significant for this function. It is recognized that some wetland islands may when
positioned offshore in close proximity to the shoreline reduce wave action and contribute to
shoreline stabilization.
For this function, the following relationships are used:
High Estuarine vegetated wetlands (except island types), Estuarine
nonvegetated irregularly flooded, Lotic wetlands (vegetated except
island and isolated types and floating mats), Lentic wetlands
(vegetated except island types and floating mats)
Moderate Other Estuarine nonvegetated wetlands (except island), Terrene
vegetated wetlands associated with ponds (e.g., Fringe-pond, Flat-pond,
and Basin-pond), Estuarine intertidal oyster reefs (along the
shoreline), Marine Unconsolidated Shore, Terrene Outflow
Headwater wetlands
Provision of Fish and Aquatic Invertebrate Habitat1
Wetlands are widely recognized as important habitats for many species of fish and wildlife and
there is a wide body of literature to support this claim (e.g., Mitsch and Gosselink 2007, Tiner
2005a). The assessment of potential habitat for fish and aquatic invertebrates is based on
generalities that could be refined for particular species of interest by others at a later date if
desirable. Regional and local variations will need to be accounted for on a watershed-by-watershed
basis. The criteria selected below are useful for the Georgia coastal zone and many
may be applicable nationwide, but they should be re-examined for each project area beyond the
Georgia coast to ensure accuracy and completeness. Although focused on fish and aquatic
invertebrates, wetlands identified as significant for these species are likely also significant for
other aquatic-dependent animals such as muskrat, turtles, water snakes, and numerous
amphibians.
For tidal areas, the assessment emphasizes estuarine wetlands, palustrine and riverine tidal
emergent wetlands, unconsolidated shores (tidal flats), and intertidal oyster reefs. For nontidal
regions, palustrine aquatic beds and permanently flooded and semipermanently flooded wetlands
1 This assessment is focused on wetlands, not deepwater habitats, hence the exclusion of the latter from this analysis,
despite widespread recognition that rivers, streams, and lakes are the primary habitats for fish and shellfish.
17
are ranked higher than seasonally flooded types due to the longer duration of surface water.
Semipermanently flooded wetlands along permanent waterbodies may serve as fish spawning
grounds during high flows. Many ponds (excluding wastewater ponds, for example) and the
shallow marsh-open water zone of impoundments are identified as wetlands having moderate
potential for fish and aquatic invertebrate habitat.
Shading by trees and tall shrubs moderates water temperatures for streams (Ghermandi et al.
2009, Wilkerson et al. 2006). Since water temperature is an important factor influencing fish use
of streams as well as providing food (through leaf drop) for aquatic organisms that are an
important part of the diet of juvenile and some adult fishes, forested and shrub wetlands along
streams have been rated as moderate for fish and shellfish. The streamside wetlands also serve
as vital buffers that help maintain good water quality.
Other wetlands providing significant fish habitat or benefits to their habitat may exist, but are not
identified. Such wetlands may be identified based on actual observations or culled out from site-specific
fisheries information that may be available from other sources. Moreover, all wetlands
rated as significant for the streamflow maintenance function are already considered vital to
sustaining the watershed's ability to provide lotic aquatic habitat. While these wetlands may not
serve as significant fish and shellfish habitat, they support base flows essential to keeping water
in streams for aquatic life. Terrene outflow wetlands and Lotic basin wetlands along low order
streams (e.g., orders 1-2 in Coastal Plain) often discharge cool groundwater to streams which
keeps these streams cooler in summer. Such wetlands are important for providing summer
refuges for some species.
For this function, the following relationships are used:
High Estuarine Emergent Wetland (including mixtures with other
types where emergent is the dominant class), Estuarine
Unconsolidated Shore (not irregularly flooded type), Estuarine
Intertidal Reef (oyster), Estuarine Aquatic Bed, Lacustrine Littoral
semipermanently flooded or permanently flooded (excluding
wetlands along intermittent streams), Lacustrine Littoral Aquatic
Bed, Lacustrine Littoral Unconsolidated Bottom/Vegetated
Wetland, Marine Intertidal Unconsolidated Shore (not irregularly
flooded), Palustrine semipermanently flooded (excluding wetlands
along intermittent streams; must be contiguous with a permanent
waterbody such as PUBH, L1UBH, or R2/R3UBH or be a
semipermanently flooded slough), Palustrine Aquatic Bed,
Palustrine Unconsolidated Bottom/Vegetated Wetland, Palustrine
Vegetated Wetland with a permanently flooded water regime,
Palustrine Tidal Emergent Wetland (excluding S water regime),
Ponds (PUBH… on NWI; not PUBF) associated with
semipermanently flooded or permanently flooded Vegetated
Wetland, Riverine Tidal Emergent Wetland, Riverine Tidal
Unconsolidated Shore (excluding those with an S water regime),
Riverine Tidal Aquatic Bed, Riverine Lower Perennial Aquatic
Bed, Riverine Lower Perennial Aquatic Bed
18
Moderate Estuarine Wetlands where Forested or Scrub-Shrub Wetland is
mixed with Emergent Wetland, Lentic wetlands that are PEM1C
(and contiguous with a waterbody), Lotic River or Stream wetlands
that are PEM1C (including mixtures with Scrub-Shrub or Forested
wetlands; and contiguous with a waterbody), Other Ponds and
associated Fringe wetlands (i.e., one acre or larger; specify pond
types: natural ponds, beaver ponds, and excavated or impounded
ponds that are used for aquaculture and wildlife management),
Lotic River Floodplain Basin Wetlands, Palustrine Tidal Forested
or Scrub-Shrub Wetlands mixed with Emergent Wetland with
seasonally flooded-tidal (R) or semipermanently flooded-tidal
(T) water regimes
Note: Industrial, commercial, and wastewater treatment ponds should be excluded
from this function.
Provision of Waterfowl and Waterbird Habitat
Wetlands designated as important for waterfowl (e.g., ducks, geese, and loons) and waterbirds
(e.g., wading birds, shorebirds, rails, marsh wrens, and red-winged blackbirds) are generally
those used for nesting, reproduction, or feeding. The emphasis is on the wetter wetlands and
ones that are frequently flooded for long periods. Other birds dependent on and/or living in
other wetlands (e.g., waterthrushes, veery, eastern kingbird, vireos, and warblers) are not
included in this function; they are included in the large group of animals referred to as “other
wildlife” in this assessment.
The selected wetlands include estuarine wetlands (vegetated or not), riverine emergent wetlands,
estuarine and riverine unconsolidated shores (excluding temporary flooded-tidal), palustrine tidal
and riverine tidal emergent wetlands (including emergent/shrub mixtures), semipermanently
flooded wetlands, mixed open water-emergent wetlands (palustrine and lacustrine), and aquatic
beds. Seasonally flooded lotic wetlands that are forested or mixtures of trees and shrubs
(excluding those along intermittent streams) are designated as having high potential because they
offer prime habitats for wood ducks. For this analysis, palustrine tidal scrub-shrub/emergent
wetlands and tidal forested/emergent wetlands were designated as having moderate significance
for waterfowl and waterbirds. Similar mixed wetlands dominated by emergent species, however,
are listed as having high significance, since the emergents typically represent wetter conditions
in Georgia’s tidal zone. Ponds one acre and larger were considered to have moderate potential
for providing waterfowl and waterbird habitat.2 Semipermanently flooded vegetated wetlands
that were not associated with a waterbody were rated as moderate for this function as were
seasonally flooded emergent wetlands (including mixtures with shrubs) contiguous with water
bodies.
2Ponds on wildlife management areas (e.g., refuges) should be considered to be of high significance due to their
management. Since we do not presently have the location of refuges recorded in our digital database, these ponds
may not be separated from the rest of the ponds. Hence, all ponds except industrial, commercial, stormwater
detention, wastewater treatment, and similar ponds, are designated as having moderate potential for this function.
19
For this function, the following relationships are used:
High Estuarine Aquatic Bed, Estuarine Emergent wetlands (including
mixtures with other vegetated types where EM dominates, e.g.,
EM/SS), Estuarine Unconsolidated Shore (except S water regime),
Estuarine Intertidal Reef, Lacustrine Semipermanently Flooded,
Lacustrine Littoral Aquatic Bed (and mixes where AB dominates),
Lacustrine Littoral Vegetated wetlands with an H water regime,
Lacustrine Unconsolidated Shores (F, E, or C water regimes),
Marine Unconsolidated Shore, Palustrine Semipermanently
Flooded and adjacent to a waterbody or along a slough; Palustrine
Semipermanently Flooded-Tidal, Palustrine Aquatic Bed, Palustrine
Vegetated wetlands with an H water regime, Seasonally Flooded
Palustrine wetlands impounded (all vegetation types and associated
PUB waters – natural ponds, waterfowl/wildlife impoundments, and
beaver ponds), Lotic River or Stream wetlands that are PEM1C
(including mixtures with Scrub-Shrub or Forested wetlands), Ponds
associated with Semipermanently Flooded Vegetated wetlands,
Palustrine Tidal Emergent wetlands (PEM1R and PEM1T and mixes
with other EM and with SS and FO), Riverine Tidal Emergent
wetlands, Riverine Tidal Unconsolidated Shores (except with S water
regime), Ponds associated with all of the above wetland types, Lotic
Basin or Fringe or Floodplain-basin wetlands (excluding those along
intermittent streams) that are Forested or Scrub-shrub or mixtures of
these types with C, F, R, or H water regime; Lotic wetlands that are
mixed Forested/Emergent or Unconsolidated Bottom/Forested with a
F, R, or H water regime; Palustrine Tidal Forested or Scrub-shrub
wetlands (and mixes with other types like the Lotic types) in
Estuarine reach with R or N water regime and contiguous with open
Water, Wildlife Impoundments (“wi”)
Moderate Estuarine Scrub-Shrub/Emergent wetland Oligohaline, Seasonally
Flooded-Tidal Palustrine Wetland where EM is the subordinate mixed
class (e.g., PFO1/EM1R), Ponds 1 acre or greater in size (excluding
industrial, commercial, stormwater detention, wastewater treatment,
and similar ponds), Palustrine Emergent wetlands (including mixtures
with Scrub-shrub) that are Seasonally Flooded and associated with
permanently flooded waterbodies, Other Palustrine vegetated (AB,
EM, SS, FO) wetlands that are Semipermanently Flooded, Other
Lacustrine Littoral Unconsolidated Bottom wetlands
Note: All waterfowl impoundments and associated wetlands that should be
marked with “wi” should be rated as high for this function. Ponds used
for aquaculture are excluded since management will likely deter use of these
ponds; associated wetlands should also be excluded from this function. Industrial,
commercial, and wastewater treatment ponds, lakes, and associated wetlands
should be excluded from this function.
20
Provision of Other Wildlife Habitat
The provision of other wildlife habitat by wetlands was evaluated in general terms. Species-specific
habitat requirements were not considered. In developing an evaluation method for
wildlife habitat in the glaciated Northeast, Golet (1972) designated several types as outstanding
wildlife wetlands including: 1) wetlands with rare, restricted, endemic, or relict flora and/or
fauna, 2) wetlands with unusually high visual quality and infrequent occurrence, 3) wetlands
with flora and fauna at the limits of their range, 4) wetlands with several seral stages of hydrarch
succession, and 5) wetlands used by great numbers of migratory waterfowl, shorebirds, marsh
birds, and wading birds. Golet subscribed to the principle that in general, as wetland size
increases so does wildlife value, so wetland size was important factor for determining wildlife
habitat potential in his approach. Other important variables included dominant wetland class,
site type (bottomland vs. upland; associated with waterbody vs. isolated), surrounding habitat
type (e.g., natural vegetation vs. developed land), degree of interspersion (water vs. vegetation),
wetland juxtaposition (proximity to other wetlands), and water chemistry.
For this analysis, wetlands important to waterfowl and waterbirds are identified in a separate
assessment. Emphasis for assessing "other wildlife" was placed on conditions that would likely
provide significant habitat for other vertebrate wildlife (mainly interior forest birds, amphibians,
reptiles, and non-aquatic mammals).
Opportunistic species that are highly adaptable to fragmented landscapes are not among the
target organisms, since there seems to be more than ample habitat for these species now and in
the future. Rather, animals whose populations may decline as wetland habitats become
fragmented by development are of key concern. For example, breeding success of neotropical
migrant birds in fragmented forests of Illinois was extremely low due to high predation rates and
brood parasitism by brown-headed cowbirds (Robinson 1990). Newmark (1991) reported local
extinctions of forest interior birds in Tanzania due to fragmentation of tropical forests.
Fragmentation of wetlands is an important issue for wildlife managers to address. Some useful
references on fragmentation relative to forest birds are Askins et al. (1987), Robbins et al.
(1989), Freemark and Merriam (1986), and Freemark and Collins (1992). The latter study
includes a list of area-sensitive or forest interior birds for the eastern United States. The work of
Robbins et al. (1989) addressed area requirements of forest birds in the Mid-Atlantic states and
may be useful further south along the coastal plain. They found that species such as the black-throated
blue warbler, cerulean warbler, Canada warbler, and black-and-white warbler required
very large tracts of forest for breeding. Ground-nesters, such as veery, black-and-white warbler,
worm-eating warbler, ovenbird, waterthrushes, and Kentucky warbler, are particularly sensitive
to predation which may be increased in fragmented landscapes. Robbins et al. (1989) suggest a
minimum forest size of 7,410 acres to retain all species of the forest-breeding avifauna in the
Mid-Atlantic region. Schroeder (1996) noted that to conserve regional biodiversity, maintenance
of large-area habitats for forest interior birds is essential. As mentioned previously, Robbins et
al. (1989) suggest a minimum forest size of 7,410 acres to retain all species of the forest-breeding
avifauna in the Mid-Atlantic region. Consequently, forested areas 7,000 acres and
larger that contained contiguous palustrine forested wetlands and upland forests are important for
maintaining regional biodiversity of avifauna on the Atlantic Coastal Plain based on
recommendations by Robbins et al. (1989). Forested wetlands within large forest blocks 7,000
acres or more were rated as having potential for providing high value habitat for other wildlife.
21
While many amphibians are strictly aquatic animals living in water, salamanders, spring peepers,
and chorus frogs spend most of their adult lives in other wetlands and upland habitats, but use
open-water wetlands (including vernal pools) for breeding. For these species, small isolated
permanently flooded or semipermanently flooded wetlands (including ponds) in an upland forest
matrix (e.g., woodland vernal pools) have been rated as having high habitat value and other
wetlands contiguous to or within 100m of these wetlands have also been similarly rated.
Although this assessment focuses on wetlands, it is important to recognize that upland forests
adjacent to these breeding ponds are prime habitats for the juveniles and adults of these species.
Many terrestrial mammals make use of wetlands including rabbits, raccoons, and deer. For these
animals, large wetlands (> 20 acres) regardless of vegetative cover but excluding pine
plantations and smaller diverse wetlands (10-20 acres with multiple cover types) have been rated
as high value. Freshwater wetlands on or near back-barrier islands (including major hammocks)
are particularly valuable habitat for numerous island wildlife. Any remaining vegetated
wetlands are designated as having moderate value for providing wildlife habitat.
Please note that with the exception of vernal pools (woodland ponds), ponds are not listed as
important as significant for "other wildlife." Wildlife species living in ponds, such as several
species of frogs and turtles, are mentioned in the discussion of fish and aquatic invertebrate
habitat, since wetlands designated as important for fish and invertebrates provide required
habitat for these species.
High *Forested wetlands within 7000-acre blocks of forest, vegetated
wetlands >20 acres (excluding open water, nonvegetated areas, and
pine plantations), small diverse wetlands (10-20 acres with 2 or
more covertypes; excluding open water as one of the covertypes),
*small isolated permanently flooded or semipermanently flooded
wetlands within an upland forest matrix (including small ponds
that may be vernal pools) and contiguous wetlands, small vegetated
wetlands on or near coastal back-barrier islands (including those on
major hammocks)
Moderate Other vegetated wetlands
*Not identified for the coastal county project.
Given the general nature of this assessment of "other wildlife habitat," other individuals may
want to refine this assessment in the future by having biologists designate "target species" that
may be used to identify important wildlife habitats in a particular watershed. After doing this,
they could identify criteria that may be used to identify potentially significant habitat for these
species in the watershed.
22
Provision of Unique, Uncommon, or Highly Diverse Wetland Plant Communities
This function is used to identify wetlands that are unique or uncommon wetland types in a
watershed or other study area, or that represent highly diverse plant communities. All riverine
and palustrine tidal emergent and scrub-shrub wetlands (regularly flooded, seasonally flooded-tidal,
and semipermanently flooded-tidal) and estuarine oligohaline vegetated wetlands are
identified as significant for this function because they often possess some of the most diverse
wetland plant communities along the Atlantic Coast. While Phragmites-dominated wetlands are
generally excluded from this listing, any wetland supporting stands of the native species should
be recognized as a significant habitat. While this type was not mapped during the updated
inventory, it may be added from documented occurrences if desirable. Generally, however, the
use of Natural Heritage Program data and other data are beyond the scope of this remotely
sensed approach to wetland functional analysis. Consequently, wetlands designated as
potentially significant for this function by the W-PAWF assessment are simply a starting point
or, in other words, a foundation to build upon. Local knowledge of significant wetlands and
Natural Heritage Program data can be applied by others to further refine the list of wetlands
important for this function for specific geographic areas.
The following are examples of wetland types viewed as potentially significant for the provision
of habitat for unique or diverse wetland plant communities in coastal Georgia (Note: The ones
underlined were identified during the inventory):
Significant Estuarine oligohaline vegetated wetlands
Riverine tidal emergent wetlands (including tidal flats that are often
colonized by nonpersistent plants during the growing season)
Palustrine tidal emergent wetlands (regularly flooded, seasonally flooded
tidal, and semipermanently flooded-tidal water regimes)
Palustrine tidal scrub-shrub wetlands (regularly flooded, seasonally
flooded-tidal, and semipermanently flooded-tidal water regimes)
Freshwater vegetated wetlands on barrier islands (semipermanently
flooded, semipermanently flooded-tidal, and permanently flooded)
Brackish marshes at upper edge of salt marshes
Stands of native Phragmites (Note: These stands have not been identified
in the wetland mapping, but can be identified from our sources.)
Carolina bay wetlands (relatively intact)
Palustrine vegetated wetlands permanently flooded
.
23
Summary
The State of Georgia has added descriptors for landscape position, landform, and water flow path
to its updated wetland digital database for six coastal counties. When LLWW descriptors are
combined with typical NWI attributes from Cowardin et al. 1979 (system, subsystem, class,
subclass, water regime, and special modifiers), a NWIPlus database is created. It contains many
properties for each wetland that can be used to produce a preliminary landscape-level assessment
of wetland functions for large geographic areas. The subject report provides the rationale for the
criteria used to identify wetlands of potential significance for eleven functions. These functions
include: 1) surface water detention, 2) coastal storm surge detention, 3) streamflow maintenance,
4) nutrient transformation, 5) carbon sequestration, 6) sediment and other particulate retention,
7) bank and shoreline stabilization, 8) provision of fish and aquatic invertebrate habitat, 9)
provision of waterfowl and waterbird habitat, 10) provision of other wildlife habitat, and 11)
provision of habitat for unique, uncommon, or highly diverse wetland plant communities. The
preliminary nature of this type of functional assessment must be emphasized and while it
provides a valuable landscape-level perspective on wetland functions, field investigations are
required to refine these findings for specific wetlands or areas of interest.
24
Acknowledgments
The Georgia relationships between NWIPlus features and eleven functions were developed with
help from participants of the August 31, 2010 workshop at Little St. Simons Island. Jan
Mackinnon (GA DNR, Coastal Resources Division) was instrumental in organizing the
workshop. Workshop participants included: Chandra Franklin (Savannah State University),
Clark Alexander (Skidaway Institute of Oceanography), Dorset Hurley (Sapelo Island National
Estuarine Research Reserve), Dominic Guadagnoli (GA DNR), Gabe Gaddis (GA DNR), Deb
Barreiro (GA DNR), Karl Burgess (GA DNR), Jill Andrews (Georgia Coastal Management
Program), Bill Wikoff (U.S. Fish and Wildlife Service), Chris Capolla (U.S. Fish and Wildlife
Service), Ralph Tiner (U.S. Fish and Wildlife Service), Brandon Moody (GA DNR
Environmental Protection Agency), Brad Winn (GA DNR Wildife Resources Division), Shelly
Krueger (University of Georgia, Marine Extension Service), Amanda Wrona (The Nature
Conservancy), Kelly O’Rourke (Georgia Coastal Management Program), Sonny Emmert
(Georgia Coastal Management Program), Dale Caldwell (GA Environmental Protection
Division), Jeb Byers (University of Georgia, Odum School of Ecology), Risa Cohen (Georgia
Southern University), Katy Freas (U.S. Army Corps of Engineers), Rhonda Evans (U.S.
Environmental Protection Agency, Region IV), Tony Able (U.S. Environmental Protection
Agency, Region IV), John Hefner (Atkins North America, formerly PBS&J, Raleigh, NC), Dave
O’Loughlin (Atkins North America), Rainor Gresham (Atkins North America), Ben Cogdell
(Atkins North America), Keith Parsons (GA Environmental Protection Division), Steve Calver
(U.S. Army Corps of Engineers Planning Division), Susan Reeves (GA DNR), Jan Mackinnon,
and Scott Coleman (Little St. Simons Island).
The draft document was reviewed by personnel from Atkins North America and the GA DNR’s
Coastal Resources Division. Rainor Gresham provided a listing of the wetland types that were
mapped in the study area for each wetland function. This information was used to highlight
those wetlands in the listing of potential wetlands of significance for each function.
The foundation for the wetland characteristics-function relationships was laid over the past 15
years and many people had a hand in the process and were recognized in the 2003 correlation
report for the Northeast (Tiner 2003b). Since then additional peer review comments were
subsequently provided by Dr. Robert Brooks (Pennsylvania State University), Dr. Christopher
Cirmo (Cortland State University), Dr. Andrew Baldwin (University of Maryland), Dr. Mark
Brinson (East Carolina University), Dr. Donald Leopold (State University of New York-
Syracuse), Matt Schweisberg (U.S. EPA, Region 1), Dr. Charles Roman (U.S. Geological
Survey, University of Rhode Island), and Dr. Aram Calhoun (University of Maine). Their
comments were helpful in improving the document.
25
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Click tabs to swap between content that is broken into logical sections.

Cover: Salt marsh on Little St. Simons Island (R. Tiner photograph).
Predicting Wetland Functions at the Landscape Level
for Coastal Georgia Using NWIPlus Data
Ralph W. Tiner
Regional Wetland Coordinator
U.S. Fish & Wildlife Service
Northeast Region
300 Westgate Center Drive
Hadley, MA 01035
Prepared In Cooperation With the
Georgia Department of Natural Resources
Coastal Resources Division, Brunswick, GA and
Atkins North America, Raleigh, NC
August 2011
This publication should be cited as:
Tiner, R.W. 2011. Predicting Wetland Functions at the Landscape Level for Coastal Georgia
Using NWIPlus Data. U.S. Fish and Wildlife Service, National Wetlands Inventory Program,
Region 5, Hadley, MA. In cooperation with the Georgia Department of Natural Resources,
Coastal Resources Division, Brunswick, GA and Atkins North America, Raleigh, NC. 29 pp.
Table of Contents
Page
Introduction 1
Creating the NWIPlus Database 4
Limitations of the Preliminary Wetland Functional Assessment 6
Rationale for Preliminary Functional Assessments 8
Surface Water Detention 9
Coastal Storm Surge Detention 10
Streamflow Maintenance 10
Nutrient Transformation 12
Carbon Sequestration 14
Retention of Sediment and Other Particulates 15
Bank and Shoreline Stabilization 16
Provision of Fish and Aquatic Invertebrate Habitat 16
Provision of Waterfowl and Waterbird Habitat 18
Provision of Other Wildlife Habitat 20
Provision of Habitat for Unique, Uncommon, or Highly Diverse
Plant Communities 22
Summary 23
Acknowledgments 24
References 25
This page is intentionally blank.
1
Introduction
The Georgia Department of Natural Resources (GA DNR) has recently updated National
Wetlands Inventory (NWI) data for the state’s six coastal counties. The U.S. Fish and Wildlife
Service (Service) has recognized the potential application of NWI data for watershed
assessments, but realized that other attributes would have to be added to the data to facilitate
functional analysis. In the early 1990s, Dr. Mark Brinson conceived a hydrogeomorphic
approach to wetland functional assessment that uses comparison of field-verified properties of
existing wetlands to those from a set of reference wetlands as a means of assessing a wetland’s
proximity to or departure from reference condition (Brinson 1993a). This approach provided the
impetus for the Service to develop other attributes to expand the NWI database and make it more
useful as a tool for landscape-level functional assessment of wetlands.
In the mid-1990s, the NWI developed a set of abiotic descriptors to describe a wetland's
landscape position, landform, water flow path, and waterbody type (LLWW descriptors; Tiner
1995, 1996a, b). Use of the initial set of keys for pilot watershed projects led to a refinement and
expansion of the keys in subsequent years (Tiner 1997a, b, 2000, 2002, 2003a). The expanded
NWI database is called NWIPlus because it significantly increases the amount of information
collected for mapped wetlands (Tiner 2010). These data allow for improved characterization of
wetlands across the landscape and make it possible to predict wetland functions at the landscape,
watershed, or regional scale. Numerous projects have created NWIPlus data and used the data to
better describe wetlands in watersheds or other specific geographic areas and produce
preliminary assessments of wetland functions (Table 1). In conducting these studies in the
Northeast, the Service worked with local and regional wetland experts to develop relationships
between wetland characteristics recorded in the database and wetland functions. The results
reflect our best approximation of what types of wetlands are likely to perform certain functions
at significant levels based on the characteristics in the NWIPlus database. Besides the Service’s
applications of these techniques, several states have been building NWIPlus or similar databases
or have plans to conduct at least a pilot study including Kansas, Michigan, Minnesota, Montana,
New Mexico, and Wisconsin (Tiner 2010). The State of Delaware has worked with the Service
to update NWI data and create a statewide NWIPlus database, and will use the information to
produce a series of reports on wetland status, recent and historic trends, wetland functions, and
potential wetland restoration sites.
2
Table 1. Areas where the Service created a NWIPlus database and where functions have been
analyzed or are planned for analysis. (* - functional assessment planned for 2011.)
State Project Area Approximate Area
(square miles)
Alaska Anchorage C7 quadrangle* 232
California Ventura River watershed 232
Connecticut entire state (planned)* 4,900
Delaware entire state* 1,900
Nanticoke watershed 490
Maine Casco Bay 1,216
Maryland Coastal Bays watershed 296
Nanticoke watershed 323
Massachusetts Boston Harbor and vicinity 232
Cape Cod and the Islands 665
Minnesota Fond du Lac reservation* 158
Mississippi Coastal zone* 1,450
New Jersey entire state* 7,500
Hackensack River watershed 197
New York Greater Buffalo area* 1,200
Catherine Creek watershed 100
Catskill watershed 571
Croton watershed 391
Cumberland Bay watershed 55
Delaware River watershed 1,013
Hackensack River watershed 197
Hudson River-Snook Kill watershed 254
Peconic River watershed 92
Post Creek-Sing Sing Creek watershed 59
Salmon River-So. Sandy Creek watershed 117
Sodus Creek watershed 54
Sodus Bay-Wolcott Creek watershed 65
Sucker Brook-Grass River watershed 124
Upper Tioughnioga River watershed 270
Upper Wappinger Creek watershed 136
Long Island* 1,400
Pennsylvania Delaware River and Lake Erie coastal zones 113
Rhode Island entire state* 1,100
South Carolina Horry and Jasper Counties* 3,100
Texas Corpus Christi area* 1,900
Vermont Southern part of state* 580
Wyoming Shirley Basin* 290
3
The State of Georgia recently added LLWW descriptors to their updated wetland inventory data
to create an NWIPlus database for six coastal counties. The NWIPlus data will be used to better
characterize wetlands in this region and to be able to predict wetland functions at the landscape
level. In order to do the latter, the relationships (formerly called correlations) developed for use
in the northeastern United States were introduced to and reviewed by a group of Georgia
scientists from federal, state, and local agencies, non-profit organizations, and academic
institutions at an August 31, 2010 workshop on Little St. Simons Island. The peer group
provided comments that were used to re-evaluate the relationships and tailor them to coastal
Georgia. In cases where there were differences in opinions, the points were considered and
decisions were made by consensus between the Coastal Resources Division of the Georgia
Department of Natural Resources, Atkins North America (formerly PBS&J Inc., Raleigh, NC),
and Ralph Tiner (U.S. Fish and Wildlife Service, Region 5, Hadley, MA).
The purpose of this report is to explain how the NWIPlus data could be and was used for
predicting wetland functions at the landscape-level for coastal Georgia and the rationale for
assigning certain biotic and/or abiotic characteristics to eleven wetland functions: 1) surface
water detention, 2) coastal storm surge detention, 3) streamflow maintenance, 4) nutrient
transformation, 5) carbon sequestration, 6) sediment and other particulate retention, 7) bank and
shoreline stabilization, 8) provision of fish and aquatic invertebrate habitat, 9) provision of
waterfowl and waterbird habitat, 10) provision of other wildlife habitat, and 11) provision of
habitat for unique, uncommon or highly diverse wetland plant communities.
4
Creating the NWIPlus Database
A set of abiotic attributes have been developed to increase the information contained in the NWI
database and to create a NWIPlus database. Four groups of attributes describe:
• landscape position (relationship of a wetland to a waterbody if present: marine—ocean,
estuarine—tidal brackish, lotic—river/stream, lentic—lake/reservoir, and terrene—not
significantly affected by such waters, or no waterbody present, or the source of a stream);
• landform (physical shape of the wetland—basin, flat, floodplain, fringe, island, and
slope);
• water flow path (inflow, outflow, throughflow, isolated, bidirectional-nontidal, and
bidirectional-tidal); and
• waterbody type (different types of estuaries, rivers, lakes, and ponds).
Collectively, they are known as LLWW descriptors, which represent the first letter of each
descriptor (landscape position, landform, water flow path, and waterbody type). Dichotomous
keys have been developed to interpret these attributes (Tiner 2003b; they will be amended in
2011 to reflect results of recent applications). Other modifiers are also included in these keys to
further describe wetland characteristics. LLWW descriptors are added to the NWI database by
interpreting topography from digital raster graphics (DRGs) or digital elevation model data
(DEMs), stream courses from the National Hydrography Dataset (NHD) and/or aerial imagery,
and waterbody types from aerial imagery (Figure 1). The interpretations are done by employing
some automated GIS-routines coupled with manual review and interpretation by wetland
specialists. This effort now increases the NWI workload by less than 10 percent.
The NWIPlus database adds value and increases the functionality of the original NWI database.
Besides providing more features that can be used to predict wetland functions from the NWI
database, NWIPlus makes it possible to better characterize the nation’s wetlands. For example,
all the palustrine wetlands, which account for 95 percent of the wetlands in the conterminous
United States, can now be linked to rivers, streams, lakes, and ponds where appropriate, so that
the acreage of floodplain wetlands, lakeside wetlands, and geographically isolated wetlands can
be reported. The Wetlands Subcommittee of the Federal Geographic Data Committee (FGDC)
recognized the value added by the LLWW descriptors and recommended that they be included in
wetland mapping to increase the functionality of wetland inventory databases (FGDC Wetlands
Subcommittee 2009).
5
Figure 1. Examples of application of LLWW descriptors to nontidal wetlands. Coding:
Landscape position = LE – Lentic, TE – Terrene, LR – Lotic River, LS – Lotic Stream;
Landform = BA – Basin, FP – Floodplain, FR – Fringe, SL – Slope; Water Flow Path = BI –
Bidirectional-nontidal, IS – Isolated, OU – Outflow, TH – Throughflow; Other descriptors: PD –
Pond, LK – Lake, hw – headwater, and pd – pond-bordering wetland. Note: If desired, ponds
and lakes can be further classified with landscape position resulting in codes of TEPDIS for the
isolated ponds and LSLKTH for the lake shown in this figure.
6
Limitations of the Preliminary Wetland Functional Assessment
Source data are a primary limiting factor for landscape-level functional assessment. NWI digital
data and existing stream data (e.g., National Hydrography Dataset) are used as the foundation for
these assessments. All wetland and stream mapping has limitations due to scale, photo quality,
date of the survey, and the difficulty of photointerpreting certain wetland types (especially
evergreen forested wetlands and drier-end wetlands; see Tiner 1997c, 1999 for details) and
narrow or intermittent streams especially those flowing through dense evergreen forests and
beneath built-up lands.
Recognizing source data limitations, it is equally important to understand that this type of
functional assessment is a preliminary one based on wetland characteristics interpreted through
remote sensing and using the best professional judgment of various specialists to develop
relationships between wetland characteristics in the database and wetland functions. It is
designed for landscape- or watershed-level assessments covering large geographic areas.
Wetlands are rated based on their biotic or abiotic characteristics as having high or moderate
potential for supporting a wetland function. Wetlands not assigned a rating are assumed to have
little or no potential for providing such function at a significant level. The ratings are based on a
review of the literature and best professional judgment by numerous scientists studying wetlands
from public agencies, private non-government organizations, and academia. Also, no attempt is
made to produce a more qualitative ranking for each function (comparing to a “reference” type
representing a wetland of the type in the ���best” condition, or on size or the degree to which it
actually performs a function given opportunity and adjacent land uses) or for each wetland based
on multiple functions as this would require more input from others and more data, well beyond
the scope of this type of broad-scale evaluation. For a technical review of wetland functions, see
Mitsch and Gosselink (2007) and for a broad overview, see Tiner (2005a).
Functional assessment of wetlands can involve many parameters. Typically such assessments
have been done in the field on a case-by-case basis, considering observed features relative to
those required to perform certain functions or by actual measurement of performance. The
preliminary assessments based on remotely sensed information do not seek to replace the need
for field evaluations since they represent the ultimate assessment of the functions for individual
wetlands. Yet, for a watershed analysis, basin-wide field-derived assessments are not practical,
cost-effective, or even possible given access considerations. For watershed planning purposes, a
more generalized assessment (level 1 assessment) is worthwhile for targeting wetlands that may
provide certain functions, especially for those functions dependent on landscape position,
landform, hydrologic processes, and vegetative life form (Brooks et al. 2004). Subsequently,
these results can be field-verified when it comes to actually evaluating particular wetlands for
acquisition purposes (e.g., for conserving biodiversity or for preserving flood storage capacity)
or for project impact assessment. Current aerial photography may also be examined to aid in
further evaluations (e.g., condition of wetland/stream buffers or adjacent land use) that can
supplement the preliminary assessment.
The landscape-level functional assessment approach -"Watershed-based Preliminary Assessment
of Wetland Functions" (W-PAWF) - applies general knowledge about wetlands and their
functions to develop a watershed overview that highlights possible wetlands of significance in
terms of performance of various functions. To accomplish this objective, the relationships
7
between wetlands and various functions are simplified into a set of practical criteria or
observable characteristics. Such assessments may be further expanded to consider the condition
of the associated waterbody and the neighboring upland or to evaluate the opportunity a wetland
has to perform a particular function or service to society, for example.
W-PAWF does not account for the opportunity that a wetland has to provide a function resulting
from a certain land-use practice upstream or the presence of certain structures or land-uses
downstream. For example, two wetlands of equal size and like vegetation may be in the right
landscape position to retain sediments. One, however, may be downstream of a land-clearing
operation that has generated considerable suspended sediments in the water column, while the
other is downstream from an undisturbed forest. The former should be actively performing
sediment trapping in a major way, whereas the latter is not. Yet if land-clearing takes place in
the latter area, the second wetland will likely trap sediments as well as the first wetland. The
entire analysis typically tends to ignore opportunity since such opportunity may have occurred in
the past or may occur in the future and the wetland is there to perform this service at higher
levels when necessary.
W-PAWF also does not consider the condition of the adjacent upland (e.g., level of disturbance)
or the actual water quality of the associated waterbody that may be regarded as important metrics
for assessing the health of individual wetlands. Collection and analysis of these data may be
done as a follow-up investigation, where desired.
It is important to re-emphasize that the preliminary assessment does not obviate the need for
more detailed assessments of the various functions and assessment of wetland condition and
opportunities to provide more benefits given the state of the contributing watershed and adjacent
land use activities. This preliminary assessment should be viewed as a starting point for more
rigorous assessments, since it attempts to cull out wetlands that may likely provide significant
functions based on generally accepted principles and the source information used for this
analysis. This assessment is most useful for regional or watershed planning purposes, for a
cursory screening of sites for acquisition, and to aid in developing landscape-level wetland
conservation and protection strategies. It can also be used to evaluate cumulative impacts on
wetlands on key functions as was done for the Nanticoke River watershed on the Delmarva
Peninsula (Tiner 2005b) or to consider the national and regional-scale impacts of policy changes
on certain wetland types (e.g., geographically isolated wetlands or headwater wetlands, or
determining significant nexus to waters of the United States). For site-specific evaluations,
additional work will be required, especially field verification and collection of site-specific data
for potential functions (e.g., following the hydrogeomorphic assessment approach as described
by Brinson 1993a or other onsite evaluation procedures, e.g., rapid field assessment). This is
particularly true for assessments of fish and wildlife habitats and biodiversity. Other sources of
data may exist to help refine some of the findings of this report (e.g., state natural heritage data).
Additional modeling could be done, for example, to identify habitats of likely significance to
individual species of animals based on their specific life history requirements (see U.S. Fish and
Wildlife Service 2003 for Gulf of Maine habitat analysis).
Also note that the criteria used for the relationships were based on Georgia’s application of the
Service's wetland classification (Cowardin et al. 1979). Regional applications of this system
may differ slightly depending on regional priorities, level of field effort, and knowledge of
wetland ecology. Use of the relationships in other regions of the country therefore may require
some adjustment based on these considerations.
8
Through this analysis, numerous wetlands are predicted to perform a given function at a
significant level presumably important to a watershed's ability to provide that function.
"Significance" is a relative term and is used in this analysis to identify wetlands that are likely to
perform a given function at a high or moderate level. It is also emphasized that the assessment is
limited to wetlands (i.e., areas classified as wetlands on NWI maps). Deepwater habitats and
streams were not included in the assessment, although their inherent value to wetlands and many
wetland-dependent organisms is apparent.
Rationale for Preliminary Functional Assessments
The W-PAWF approach (“watershed-based preliminary assessment of wetland functions”) is
intended to produce a more expansive characterization of wetlands and their likely functions and
data that can be used to help rank wetlands for acquisition, protection, or other purposes.
Presently, a maximum of eleven functions may be evaluated: 1) surface water detention, 2)
coastal storm surge detention, 3) streamflow maintenance, 4) nutrient transformation, 5) carbon
sequestration, 6) sediment and other particulate retention, 7) bank and shoreline stabilization, 8)
provision of fish and aquatic invertebrate habitat, 9) provision of waterfowl and waterbird
habitat, 10) provision of other wildlife habitat, and 11) provision of habitat for unique,
uncommon, or highly diverse wetland plant communities. The criteria used for identifying
wetlands of significance for each of these functions using Georgia’s NWIPlus database are
discussed below. The criteria and ratings were initially developed for northeastern wetlands by
the author of this report based on his knowledge of wetland characteristics and functions. The
draft criteria were then reviewed and modified for various watersheds based on comments from
wetland specialists working on specific watersheds in four Northeast states (Maine, New York,
Delaware, and Maryland). While many of the criteria are universally applicable, when applying
NWIPlus data to other regions for landscape-level functional assessment, the criteria and ratings
should be reviewed. For coastal Georgia, a workshop sponsored by the Georgia Department of
Natural Resources was conducted on August 31, 2010 to get input from local experts on the
applicability of these relationships for tidal and nontidal wetlands in six coastal counties (see
Acknowledgments for participants). The actual application of the Cowardin et al. (1979)
classification also needed to be considered as there may be differences in the level of
classification for individual projects, such as the use of water regime indicators that could affect
functional ratings.
In developing a protocol for designating wetlands of potential significance, wetland size was
generally disregarded from the criteria, with few exceptions (i.e., other wildlife habitat and
biodiversity functions). This approach was followed because it was felt that individual agencies
and organizations using the digital database and charged with setting priorities should make the
decision on appropriate size criteria as a means of limiting the number of priority wetlands as
necessary. There is no science-based size limit to establish significance for any function.
However, it is obvious that, all things being equal, a larger wetland will have a higher capacity to
perform a given function than a smaller one of the same type, although it is recognized that
certain wildlife species (e.g., amphibians) require a multitude of small wetlands to maintain their
local populations given vagaries of weather and its effect on habitat suitability.
9
After discussing a particular function and the wetland types that are likely to perform that
function, a list of wetland types is given for two levels of function. These types were determined
to have the potential to perform the subject function at a significant level.
ATTENTION: The types that are underlined are types that were actually mapped during the
inventory and will be displayed on the wetland function maps for coastal Georgia. The other
types (not underlined) are other wetlands that may perform that function at the specified level,
however no wetlands were classified as these types during this survey.
Surface Water Detention
This function is important for reducing downstream flooding and lowering flood heights, both of
which aid in minimizing property damage and personal injury from such events. In a landmark
study on the relationships between wetlands and flooding at the watershed scale, Novitzki (1979)
found that watersheds with 40 percent coverage by lakes and wetlands had significantly reduced
flood flows -- lowered by as much as 80 percent -- compared to similar watersheds with no or
few lakes and wetlands in Wisconsin. The same principles apply to Georgia where studies have
shown that watersheds with an abundance of wetlands moderate flood flows more than those
with less wetland (Wharton 1970). After heavy rains, the former watersheds take longer to reach
peak water levels and have less fluctuation than the latter watersheds which reach their peaks
more quickly, produce higher peaks, and tend to have more swift flows.
For purposes of landscape-level functional assessment following W-PAWF, this function will be
restricted to surface water storage of nontidal waters. Floodplain wetlands and other lotic
wetlands (basin and flat types) provide this function at significant levels. While tidal wetlands
along rivers serve at times to attenuate freshwater flood flows from upstream watersheds, they are
excluded from this function because they are subjected to frequent tidal flooding. The water
storage function of tidal wetlands for detaining storm surges is evaluated separately via the coastal
storm surge detention function. Stormwater detention ponds are designed for temporary storage of
surface water and are recognized as having a high level of performance for this function.
Wetlands dominated by trees and/or dense stands of shrubs could be deemed to provide a higher
level of this function than emergent wetlands, since woody vegetation (with higher frictional
resistance) may further aid in flood desynchronization. However, emergent wetlands along
waterways provide significant flood storage, so no distinction is made regarding the type of
vegetative cover. Floodplain width could also be an important factor in evaluating the
significance of performance of this function by individual wetlands (e.g., for acquisition or
strengthened protection), but there is no scientifically based criterion for establishing a
significance threshold based on size. Drier-end wetlands (e.g., flats), and isolated basins are
rated as having moderate potential.
For this function, the following relationships are used:
High Lentic Basin, Lentic Fringe, Lentic Island (basin and fringe),
Lentic Flat associated with reservoirs and flood control dams,
Lotic Stream Basin, Lotic Floodplain-basin, Lotic River Fringe,
Lotic Stream Fringe (not “A” water regime), Lotic River Island-basin,
Ponds Throughflow (in-stream) and associated Fringe and
Basin wetlands, Terrene Throughflow Basin, Stormwater
Treatment Ponds
10
Moderate Lotic River Floodplain-flat, Lotic River Fringe (other than above),
Lotic Stream Fringe (other than above), Lotic Stream Flat, Lotic
River Island-flat, Lentic Flat, Other Terrene Basins, Other Ponds
and associated wetlands (excluding sewage treatment ponds and
isolated impoundments), Terrene wetland associated with ponds
(TE__pd__, excluding isolated diked ponds), Terrene Flat
Note: Exclude the following: 1) artificially flooded wetlands (“K” water regime,
unless they are in a reservoir or dammed lake), 2) isolated impounded ponds and
associated wetlands, 3) any freshwater tidal wetlands that are in the Lotic
landscape position, and 4) any seasonally saturated wetlands (“B” water regime)
from this function.
Coastal Storm Surge Detention
This function is listed separately from Surface Water Detention to highlight the importance of
tidal wetlands and adjacent lowland wetlands at storing tidal waters brought into estuaries by
storms (e.g., tropical storms and hurricanes). Estuarine and freshwater tidal wetlands are
important areas for temporary storage of this water. Some nontidal wetlands contiguous to these
wetlands (e.g., low-lying terrene outflow basins - flatwoods) may also provide this function, but
do so only during the most extreme storm events, so they were rated as moderate for this
function. Note that tidal wetlands along rivers may also be important for attenuating freshwater
floodwaters resulting from heavy precipitation events upstream in the watershed.
For this function, the following relationships are used:
High Estuarine Basin, Estuarine Fringe, Estuarine Island, Lotic Tidal
Fringe, Lotic Tidal Island, Lotic Tidal Floodplain, Marine Fringe,
Marine Island
Moderate Other tidal wetlands not included above plus any Terrene wetland
(excluding SL – slope wetland) with “ed” modifier (nontidal
wetlands contiguous with estuarine wetlands discharging and likely
subject to infrequent or occasional flooding by storm tides) or with
“ow” modifier (overwash)
Streamflow Maintenance
There are four main sources of water to support stream flow: 1) groundwater, 2) interflow
through the soil, 3) precipitation, and 4) surface water runoff. Groundwater provides water for
base flows. Many wetlands are sources of groundwater discharge and those located in headwater
positions either the source of streams or along low-order perennial streams contribute
significantly to sustain streamflow in the watershed. Such wetlands are critically important for
supporting aquatic life in streams. The importance of maintaining natural streamflow patterns is
important to riparian vegetation as well as to resident aquatic species and altering those patterns
can negatively impact local biodiversity (Cowell and Stoudt 2002).
11
All wetlands classified as headwater wetlands are important for streamflow. Terrene headwater
wetlands, by definition, are sources of streams. They contribute groundwater (base flow) from
local unconfined aquifers and regional confined aquifers to support streamflow (Priest 2004).
Other headwater wetlands include lotic wetlands along 1st-order streams and lentic wetlands
associated with outflow lakes. Wetlands along 2nd-order streams in mountainous areas may be
classified as headwater wetlands as they probably are sites of groundwater discharge, but these
conditions do not apply to the Georgia coastal region since Georgia’s mountains are much
further inland. Ditched headwater wetlands are rated as moderate, since this alteration typically
results in faster release of water, thereby reducing the period of outflow. Outflow from
groundwater-fed wetlands (lacking a stream) may discharge directly into streams and thereby
contribute variable quantities of water for sustaining baseflows. These wetlands were rated as
moderate for this function. Lakes may also be important regulators of streamflow, so lentic
wetlands may be designated as significant to streamflow, with those in headwater positions being
rated high and others as moderate.
Floodplain wetlands are known to store water in the form of bank storage, later releasing this
water to maintain baseflows (Whiting 1998). Among several key factors affecting bank storage
are porosity and permeability of the bank material, the width of the floodplain, and the hydraulic
gradient (steepness of the water table). It is recognized that the wider the floodplain, the more
bank storage given the same soils. Gravel floodplains drain in days, sandy floodplains in a few
weeks to a few years, silty floodplains in years, and clayey floodplains in decades. In good
water years, wide sandy floodplains may help maintain baseflows. Bank stratigraphy is another
factor that could be considered important for streamflow maintenance (Christopher Cirmo, pers.
comm. 2006). For example, the presence of a “sand” layer between clay layers (such as in a
system where there have been historical floods) may affect the transmissivity of the bank. Bank
storage may serve to maintain streamflow in some fringe or floodplain wetlands, however a
rudimentary knowledge of the surficial stratigraphy is not normally available based solely on
remote data interpretation. Despite the variability in floodplain properties, the W-PAWF
assessment treats all nontidal floodplain wetlands and stream basins as having potential to
support streamflow, since remote sensing data does not include soil examinations or bank
stratigraphy and there is no recognized floodplain width designated to separate high from
moderate potential.
While diked ponds may contribute to streamflow when water overflows spillways or exceeds
height of water-control structures, these ponds typically reduce streamflow (McMurray 2007,
Van Liew 2004). However, some ponds may extend storm-flow over longer durations by
reducing peak flows (Bosch et al. 2003). Since impounded ponds are artificially created waters
that substantially alter natural streamflow characteristics they are not included as significant for
streamflow maintenance.
For this function, the following relationships are used:
High Unaltered Headwater Wetlands and Headwater Ponds (latter are
natural ponds not created or altered)
12
Moderate Ditched or excavated Headwater Wetlands (not impounded), Lotic
River (nontidal) Floodplain (excluding impounded or ditched),
Lotic Stream (nontidal) Basin (excluding impounded or ditched),
Terrene Basin Outflow wetlands (associated with streams not
major rivers; excluding impounded or ditched)
Note: Diked wetlands and ponds and excavated ponds should be excluded from this function.
Special Note: All wetlands important for streamflow maintenance should be considered to also
be important for fish and aquatic invertebrates as they are vital to sustaining streamflow
necessary for the survival of these aquatic organisms.
Nutrient Transformation
All wetlands recycle nutrients, but those having a fluctuating water table and corresponding
changes from aerobic to anaerobic conditions are best able to recycle nitrogen and other
nutrients. While vegetation slows the flow of water causing deposition of mineral and organic
particles with adsorbed nutrients (nitrogen and phosphorus), hydric soils are the places where
chemical transformations occur (Carter 1996). Microbial action in the soil is the driving force
behind chemical transformations in wetlands. Microbes need a food source to survive and
reproduce and in wetlands organic matter provides this needed sustenance. Wetlands with high
amounts of organic matter should have an abundance of microflora to perform the nutrient
cycling function. Wetlands are so effective at filtering and transforming nutrients that artificial
wetlands are constructed for water quality renovation (e.g., Hammer 1992). Natural wetlands
performing this function help improve local water quality of streams and other watercourses.
Oyster reefs are also recognized as important components for nitrogen cycling in estuaries
(Dame et al. 1985, Dame and Libes 1993, Fulford et al. 2010).
Numerous studies have demonstrated the importance of wetlands in denitrification. Simmons et
al. (1992) found high nitrate removal (greater than 80%) from groundwater during both the
growing season and dormant season in Rhode Island streamside (lotic) wetlands. Groundwater
temperatures throughout the dormant season were between 6.5 and 8.0 degrees C, so microbial
activity was not limited by temperature. Even the nearby upland, especially transitional areas
with somewhat poorly drained soils, experienced an increase in nitrogen removal during the
dormant season. This was attributed to a seasonal rise in the water table that exposed the upper
portion of the groundwater to soil with more organic matter (nearer the ground surface), thereby
supporting microbial activity and denitrification. Riparian forests dominated by wetlands have a
greater proportion of groundwater (with nitrate) moving within the biologically active zone of
the soil that makes nitrate available for uptake by plants and microbes (Nelson et al. 1995).
Riparian forests on well-drained soils are much less effective at removing nitrate. In a Rhode
Island study, Nelson et al. (1995) found that November had the highest nitrate removal rate due
to the highest water tables in the poorly drained soils, while June experienced the lowest removal
rate when the deepest water table levels occurred. Similar results can be expected to occur
elsewhere. For bottomland hardwood wetlands, DeLaune et al. (1996) reported decreases in
nitrate from 59-82 percent after 40 days of flooding wetland soil cores taken from the Cache
River floodplain in Arkansas. Moreover, they surmised that denitrification in these soils
appeared to be carbon-limited: increased denitrification took place in soils with more organic
matter in the surface layer. Nitrogen removal rates for freshwater wetlands are very high
(averaging from 20-80 grams/square meter) (Bowden 1987).
13
Nitrogen fixation has been attributed to blue-green algae in the photic zone at the soil-water
interface and to heterotrophic bacteria associated with plant roots (Buresh et al. 1980). In
working with rice, Matsuguchi (1979) believed that the significance of heterotrophic fixation in
the soil layer beyond the roots has been underrated and presented data showing that such zones
were the most important sites for nitrogen fixation in a Japanese rice field. This conclusion was
further supported by Wada et al. (1978). Higher fixation rates have been found in the
rhizosphere of wetland plants than in dryland plants. Nitrogen fixation converts atmospheric
nitrogen to a usable form for plants and helps enrich soils. Plants with the ability to fix nitrogen
(e.g., with symbiotic bacteria on root nodules) can thereby grow in otherwise inhospitable
nutrient-poor soils.
From the water quality standpoint, wetlands associated with watercourses are probably the most
noteworthy. Numerous studies have found that forested wetlands along rivers and streams
(Ariparian forested wetlands@) are important for nutrient retention and sedimentation during
floods (Whigham et al. 1988; Yarbro et al. 1984; Simpson et al. 1983; Peterjohn and Correll
1982). This function by forested riparian wetlands is especially important in agricultural areas.
Brinson (1993b) suggested that riparian wetlands along low-order streams may be more
important for nutrient retention than those along higher order streams.
Most of the groundwater flux from uplands to surface waters occurs in the non-growing season
in the Northeast and reasonable denitrification rates occur in spring and fall making sites that are
wet during these times important for nutrient retention (Art Gold, pers. comm. 2003). Wetlands
with seasonally flooded and wetter water regimes (including tidal regimes - seasonally flooded-tidal,
irregularly flooded, and regularly flooded) are identified as having potential to recycle
nutrients at high levels of performance. The soils of these wetlands should have substantial
amounts of organic matter near the surface to promote microbial activity and denitrification
when wet. Based on field observations, in general, there is a positive correlation between the
amount of organic matter and the degree of wetness as reflected by the NWI's water regime
classification in wetlands of the Nanticoke River watershed in Delaware (Amy Jacobs, pers.
comm. 2003). Periodically flooded soils also retain sediments and their adsorbed nutrients.
Drier-end wetlands -- those with a temporarily flooded water regime (including temporarily
flooded-tidal) and others with a seasonally saturated water regime -- are considered as having
moderate potential for performing this function, since they are relatively dry for most of the year.
For this function, relationships are the following:
High Vegetated wetlands (and mixes with nonvegetated wetlands or
unconsolidated bottom; only where vegetated predominates) with
seasonally flooded (C), semipermanently flooded (F),
semipermanently flooded-tidal (T), seasonally flooded-tidal (R),
irregularly flooded (P), regularly flooded (N), and permanently
flooded (H or L) water regimes, estuarine intertidal oyster reefs,
Vegetated wetlands with a permanently saturated water regime
Moderate Vegetated wetlands with seasonally saturated (B on the coastal
plain), temporarily flooded (A) or temporarily flooded-tidal (S)
14
water regimes; nonvegetated/vegetated wetlands (where
nonvegetated predominates) with seasonally flooded (C),
semipermanently flooded (F), semipermanently flooded-tidal (T),
seasonally flooded-tidal (R), irregularly flooded (P), regularly
flooded (N), and permanently flooded (H or L) water regimes
Carbon Sequestration
Concern over rising global temperatures and climate change has directed attention to wetlands
since they are recognized as important carbon sinks. Drainage of wetlands releases carbon to the
atmosphere in the form of carbon dioxide, one of several greenhouse gases influencing global
temperatures. In wetlands, organic matter (carbon) accumulates in the soils as well as in
vegetation. Woody plants, thereby, store carbon for longer periods than annual herbaceous
plants. While the above-ground biomass of perennial herbs is released back into the aquatic
ecosystem seasonally, the below-ground biomass remains in the substrate and contributes to
longer-term storage. Temperate and subtropical wetlands are recognized as important for
attenuating global warming (Whiting and Chanton 2001).
Interestingly, tidal salt marshes sequester up to fifty times more carbon per acre than is
sequestered by tropical forests (Pidgeon 2009). Salt marshes, unlike freshwater wetlands, do not
release significant quantities of methane (a recognized greenhouse gas contributing to global
warming) to the atmosphere (Chmura 2009). Studies in Georgia have found that among tidal
wetlands, the tidal freshwater wetlands and brackish marshes sequester more carbon and retain
more nutrients than salt marshes (Loomis and Craft 2010). In fact, tidal fresh and brackish
marshes sequestered 66 percent of the carbon and 69 percent of the nitrogen stored in all tidal
wetlands in the three-river system studied (Ogeechee, Altamaha, and Satilla) even though they
represent only 41 percent of the marsh area. Anaerobic conditions resulting from prolonged
flooding or soil saturation typically lead to an accumulation of organic matter. Therefore,
wetlands that experience longer duration of soil saturation should accumulate more organic
matter. Northern bogs that are nearly continuous saturated in boreal to arctic climates where low
evapotranspiration rates occur are recognized as major global carbon sinks. Consequently,
wetlands with the wetter water regimes (i.e., seasonally flooded and wetter) should store more
carbon than wetlands in the same region with drier water regimes that promote more oxidation
and decomposition of organic matter. Seasonally flooded and wetter vegetated wetlands are
rated as high for the carbon sequestration function, while drier wetlands (temporarily flooded
and seasonally saturated) are assigned a moderate rating. Tidal flats (unconsolidated shores,
mudflats in particular, except sandy beaches and sand flats) are listed as moderate because they
sequester carbon at lower rates than vegetated coastal wetlands (Duarte et al. 2005). Ponds were
also designated as moderate because recent studies have indicated the cumulative importance of
small ponds in sequestering carbon through sedimentation processes (Downing 2010). Several
types of ponds that are not likely to be capture organic-enriched sediment from local watersheds
are excluded from this function: aquaculture, commercial, industrial, residential-stormwater,
sewage treatment, and isolated diked ponds (impoundments).
High Tidal vegetated wetlands (including mixed with unconsolidated
shore), Nontidal vegetated wetlands that are seasonally flooded,
semipermanently flooded, or intermitttently exposed, Nontidal
vegetated wetlands that are permanently saturated
15
Moderate Nontidal vegetated wetlands that are temporarily flooded or
seasonally saturated, Tidal unconsolidated shore wetlands
(including mixes with vegetated types; focus on mudflats and
organic substrates for purely nonvegetated types; exclude sandy
beaches, sand flats, and flats with other substrates), Nontidal
nonvegetated/vegetated wetlands, Ponds (excluding aquaculture,
commercial, industrial, residential-stormwater, and sewage
treatment ponds plus isolated impoundments)
Retention of Sediment and Other Particulates
Many wetlands owe their existence to being located in areas of sediment deposition. This is
especially true for floodplain and estuarine wetlands. This function supports water quality
maintenance by capturing sediments with bonded nutrients or heavy metals as in and
downstream of urban areas (e.g., Gambrell 1994). Estuarine and floodplain wetlands plus lotic
(streamside) and lentic (lakeshore) fringe and basin wetlands including lotic (in-stream) ponds
are likely to trap and retain sediments and particulates at significant levels. Terrene throughflow
basins should function similarly. Vegetated wetlands will likely favor sedimentation over
nonvegetated wetlands and therefore they received a high rating versus moderate for the
nonvegetated types. Lotic flat wetlands are flooded only for brief periods and less frequently
than the wetlands listed above due to their elevation; they are classified as having moderate
potential for sediment retention. Throughflow (in-stream) ponds and associated fringe and basin
vegetated wetlands are rated as high, since they occur within the stream network where they trap
water-borne sediments. Stormwater treatment ponds are designed specifically to perform this
function, so they are rated as high. Other ponds and terrene basins may be locally significant in
retaining such materials, and are therefore designated as moderate. However, commercial,
industrial, residential, sewage treatment, golf, and mining ponds were not rated as significant
since many are isolated diked impoundments. Terrene flats are not rated as potentially
significant because they are level landscapes that do not appear to trap substantial amounts of
sediment from surrounding areas.
For this function, the following relationships are used:
High Estuarine vegetated (not floating mats), Lentic vegetated (not Flat
and not floating mats), Lotic vegetated (not Flat, not Floodplain-flat,
and not floating mats), Throughflow Ponds and Lakes (in-stream;
designated as PUB... on NWI) and associated vegetated
wetlands, Bidirectional-tidal Ponds and associated vegetated
wetlands, Terrene Throughflow Basin, Stormwater Treatment
Ponds
Moderate Estuarine nonvegetated (excluding rocky shore), Lotic
nonvegetated, Lotic Flat, Lotic Floodplain-flat, Lentic Flat, Marine
Fringe (excluding rocky shore), Marine Island (excluding rocky
shore), Other Terrene Basins, Terrene wetlands associated with
ponds (excluding some types of ponds - commercial,
industrial, sewage treatment, and mining), Other Ponds and Lakes
(classified as PUB... on NWI) and associated wetlands (excluding
16
some types of ponds – commercial, industrial, sewage treatment,
and mining and slope wetlands)
Bank and Shoreline Stabilization
Vegetation colonizing banks and shorelines stabilizes the soil or substrate and diminishes wave
action, thereby reducing shoreline erosion potential and increasing bank stability. Vegetated
wetlands along all flowing or large standing waterbodies (e.g., estuaries, lakes, rivers, and
streams) therefore provide this function at high levels. Intertidal oyster reefs when located along
shorelines help protect the shorelines from erosion and are therefore rated as high. Vegetated
wetlands along ponds are designated as moderate for this function since there is less wave or
erosive action along these shores. Since island wetlands are surrounded by water, they are not
considered significant for this function. It is recognized that some wetland islands may when
positioned offshore in close proximity to the shoreline reduce wave action and contribute to
shoreline stabilization.
For this function, the following relationships are used:
High Estuarine vegetated wetlands (except island types), Estuarine
nonvegetated irregularly flooded, Lotic wetlands (vegetated except
island and isolated types and floating mats), Lentic wetlands
(vegetated except island types and floating mats)
Moderate Other Estuarine nonvegetated wetlands (except island), Terrene
vegetated wetlands associated with ponds (e.g., Fringe-pond, Flat-pond,
and Basin-pond), Estuarine intertidal oyster reefs (along the
shoreline), Marine Unconsolidated Shore, Terrene Outflow
Headwater wetlands
Provision of Fish and Aquatic Invertebrate Habitat1
Wetlands are widely recognized as important habitats for many species of fish and wildlife and
there is a wide body of literature to support this claim (e.g., Mitsch and Gosselink 2007, Tiner
2005a). The assessment of potential habitat for fish and aquatic invertebrates is based on
generalities that could be refined for particular species of interest by others at a later date if
desirable. Regional and local variations will need to be accounted for on a watershed-by-watershed
basis. The criteria selected below are useful for the Georgia coastal zone and many
may be applicable nationwide, but they should be re-examined for each project area beyond the
Georgia coast to ensure accuracy and completeness. Although focused on fish and aquatic
invertebrates, wetlands identified as significant for these species are likely also significant for
other aquatic-dependent animals such as muskrat, turtles, water snakes, and numerous
amphibians.
For tidal areas, the assessment emphasizes estuarine wetlands, palustrine and riverine tidal
emergent wetlands, unconsolidated shores (tidal flats), and intertidal oyster reefs. For nontidal
regions, palustrine aquatic beds and permanently flooded and semipermanently flooded wetlands
1 This assessment is focused on wetlands, not deepwater habitats, hence the exclusion of the latter from this analysis,
despite widespread recognition that rivers, streams, and lakes are the primary habitats for fish and shellfish.
17
are ranked higher than seasonally flooded types due to the longer duration of surface water.
Semipermanently flooded wetlands along permanent waterbodies may serve as fish spawning
grounds during high flows. Many ponds (excluding wastewater ponds, for example) and the
shallow marsh-open water zone of impoundments are identified as wetlands having moderate
potential for fish and aquatic invertebrate habitat.
Shading by trees and tall shrubs moderates water temperatures for streams (Ghermandi et al.
2009, Wilkerson et al. 2006). Since water temperature is an important factor influencing fish use
of streams as well as providing food (through leaf drop) for aquatic organisms that are an
important part of the diet of juvenile and some adult fishes, forested and shrub wetlands along
streams have been rated as moderate for fish and shellfish. The streamside wetlands also serve
as vital buffers that help maintain good water quality.
Other wetlands providing significant fish habitat or benefits to their habitat may exist, but are not
identified. Such wetlands may be identified based on actual observations or culled out from site-specific
fisheries information that may be available from other sources. Moreover, all wetlands
rated as significant for the streamflow maintenance function are already considered vital to
sustaining the watershed's ability to provide lotic aquatic habitat. While these wetlands may not
serve as significant fish and shellfish habitat, they support base flows essential to keeping water
in streams for aquatic life. Terrene outflow wetlands and Lotic basin wetlands along low order
streams (e.g., orders 1-2 in Coastal Plain) often discharge cool groundwater to streams which
keeps these streams cooler in summer. Such wetlands are important for providing summer
refuges for some species.
For this function, the following relationships are used:
High Estuarine Emergent Wetland (including mixtures with other
types where emergent is the dominant class), Estuarine
Unconsolidated Shore (not irregularly flooded type), Estuarine
Intertidal Reef (oyster), Estuarine Aquatic Bed, Lacustrine Littoral
semipermanently flooded or permanently flooded (excluding
wetlands along intermittent streams), Lacustrine Littoral Aquatic
Bed, Lacustrine Littoral Unconsolidated Bottom/Vegetated
Wetland, Marine Intertidal Unconsolidated Shore (not irregularly
flooded), Palustrine semipermanently flooded (excluding wetlands
along intermittent streams; must be contiguous with a permanent
waterbody such as PUBH, L1UBH, or R2/R3UBH or be a
semipermanently flooded slough), Palustrine Aquatic Bed,
Palustrine Unconsolidated Bottom/Vegetated Wetland, Palustrine
Vegetated Wetland with a permanently flooded water regime,
Palustrine Tidal Emergent Wetland (excluding S water regime),
Ponds (PUBH… on NWI; not PUBF) associated with
semipermanently flooded or permanently flooded Vegetated
Wetland, Riverine Tidal Emergent Wetland, Riverine Tidal
Unconsolidated Shore (excluding those with an S water regime),
Riverine Tidal Aquatic Bed, Riverine Lower Perennial Aquatic
Bed, Riverine Lower Perennial Aquatic Bed
18
Moderate Estuarine Wetlands where Forested or Scrub-Shrub Wetland is
mixed with Emergent Wetland, Lentic wetlands that are PEM1C
(and contiguous with a waterbody), Lotic River or Stream wetlands
that are PEM1C (including mixtures with Scrub-Shrub or Forested
wetlands; and contiguous with a waterbody), Other Ponds and
associated Fringe wetlands (i.e., one acre or larger; specify pond
types: natural ponds, beaver ponds, and excavated or impounded
ponds that are used for aquaculture and wildlife management),
Lotic River Floodplain Basin Wetlands, Palustrine Tidal Forested
or Scrub-Shrub Wetlands mixed with Emergent Wetland with
seasonally flooded-tidal (R) or semipermanently flooded-tidal
(T) water regimes
Note: Industrial, commercial, and wastewater treatment ponds should be excluded
from this function.
Provision of Waterfowl and Waterbird Habitat
Wetlands designated as important for waterfowl (e.g., ducks, geese, and loons) and waterbirds
(e.g., wading birds, shorebirds, rails, marsh wrens, and red-winged blackbirds) are generally
those used for nesting, reproduction, or feeding. The emphasis is on the wetter wetlands and
ones that are frequently flooded for long periods. Other birds dependent on and/or living in
other wetlands (e.g., waterthrushes, veery, eastern kingbird, vireos, and warblers) are not
included in this function; they are included in the large group of animals referred to as “other
wildlife” in this assessment.
The selected wetlands include estuarine wetlands (vegetated or not), riverine emergent wetlands,
estuarine and riverine unconsolidated shores (excluding temporary flooded-tidal), palustrine tidal
and riverine tidal emergent wetlands (including emergent/shrub mixtures), semipermanently
flooded wetlands, mixed open water-emergent wetlands (palustrine and lacustrine), and aquatic
beds. Seasonally flooded lotic wetlands that are forested or mixtures of trees and shrubs
(excluding those along intermittent streams) are designated as having high potential because they
offer prime habitats for wood ducks. For this analysis, palustrine tidal scrub-shrub/emergent
wetlands and tidal forested/emergent wetlands were designated as having moderate significance
for waterfowl and waterbirds. Similar mixed wetlands dominated by emergent species, however,
are listed as having high significance, since the emergents typically represent wetter conditions
in Georgia’s tidal zone. Ponds one acre and larger were considered to have moderate potential
for providing waterfowl and waterbird habitat.2 Semipermanently flooded vegetated wetlands
that were not associated with a waterbody were rated as moderate for this function as were
seasonally flooded emergent wetlands (including mixtures with shrubs) contiguous with water
bodies.
2Ponds on wildlife management areas (e.g., refuges) should be considered to be of high significance due to their
management. Since we do not presently have the location of refuges recorded in our digital database, these ponds
may not be separated from the rest of the ponds. Hence, all ponds except industrial, commercial, stormwater
detention, wastewater treatment, and similar ponds, are designated as having moderate potential for this function.
19
For this function, the following relationships are used:
High Estuarine Aquatic Bed, Estuarine Emergent wetlands (including
mixtures with other vegetated types where EM dominates, e.g.,
EM/SS), Estuarine Unconsolidated Shore (except S water regime),
Estuarine Intertidal Reef, Lacustrine Semipermanently Flooded,
Lacustrine Littoral Aquatic Bed (and mixes where AB dominates),
Lacustrine Littoral Vegetated wetlands with an H water regime,
Lacustrine Unconsolidated Shores (F, E, or C water regimes),
Marine Unconsolidated Shore, Palustrine Semipermanently
Flooded and adjacent to a waterbody or along a slough; Palustrine
Semipermanently Flooded-Tidal, Palustrine Aquatic Bed, Palustrine
Vegetated wetlands with an H water regime, Seasonally Flooded
Palustrine wetlands impounded (all vegetation types and associated
PUB waters – natural ponds, waterfowl/wildlife impoundments, and
beaver ponds), Lotic River or Stream wetlands that are PEM1C
(including mixtures with Scrub-Shrub or Forested wetlands), Ponds
associated with Semipermanently Flooded Vegetated wetlands,
Palustrine Tidal Emergent wetlands (PEM1R and PEM1T and mixes
with other EM and with SS and FO), Riverine Tidal Emergent
wetlands, Riverine Tidal Unconsolidated Shores (except with S water
regime), Ponds associated with all of the above wetland types, Lotic
Basin or Fringe or Floodplain-basin wetlands (excluding those along
intermittent streams) that are Forested or Scrub-shrub or mixtures of
these types with C, F, R, or H water regime; Lotic wetlands that are
mixed Forested/Emergent or Unconsolidated Bottom/Forested with a
F, R, or H water regime; Palustrine Tidal Forested or Scrub-shrub
wetlands (and mixes with other types like the Lotic types) in
Estuarine reach with R or N water regime and contiguous with open
Water, Wildlife Impoundments (“wi”)
Moderate Estuarine Scrub-Shrub/Emergent wetland Oligohaline, Seasonally
Flooded-Tidal Palustrine Wetland where EM is the subordinate mixed
class (e.g., PFO1/EM1R), Ponds 1 acre or greater in size (excluding
industrial, commercial, stormwater detention, wastewater treatment,
and similar ponds), Palustrine Emergent wetlands (including mixtures
with Scrub-shrub) that are Seasonally Flooded and associated with
permanently flooded waterbodies, Other Palustrine vegetated (AB,
EM, SS, FO) wetlands that are Semipermanently Flooded, Other
Lacustrine Littoral Unconsolidated Bottom wetlands
Note: All waterfowl impoundments and associated wetlands that should be
marked with “wi” should be rated as high for this function. Ponds used
for aquaculture are excluded since management will likely deter use of these
ponds; associated wetlands should also be excluded from this function. Industrial,
commercial, and wastewater treatment ponds, lakes, and associated wetlands
should be excluded from this function.
20
Provision of Other Wildlife Habitat
The provision of other wildlife habitat by wetlands was evaluated in general terms. Species-specific
habitat requirements were not considered. In developing an evaluation method for
wildlife habitat in the glaciated Northeast, Golet (1972) designated several types as outstanding
wildlife wetlands including: 1) wetlands with rare, restricted, endemic, or relict flora and/or
fauna, 2) wetlands with unusually high visual quality and infrequent occurrence, 3) wetlands
with flora and fauna at the limits of their range, 4) wetlands with several seral stages of hydrarch
succession, and 5) wetlands used by great numbers of migratory waterfowl, shorebirds, marsh
birds, and wading birds. Golet subscribed to the principle that in general, as wetland size
increases so does wildlife value, so wetland size was important factor for determining wildlife
habitat potential in his approach. Other important variables included dominant wetland class,
site type (bottomland vs. upland; associated with waterbody vs. isolated), surrounding habitat
type (e.g., natural vegetation vs. developed land), degree of interspersion (water vs. vegetation),
wetland juxtaposition (proximity to other wetlands), and water chemistry.
For this analysis, wetlands important to waterfowl and waterbirds are identified in a separate
assessment. Emphasis for assessing "other wildlife" was placed on conditions that would likely
provide significant habitat for other vertebrate wildlife (mainly interior forest birds, amphibians,
reptiles, and non-aquatic mammals).
Opportunistic species that are highly adaptable to fragmented landscapes are not among the
target organisms, since there seems to be more than ample habitat for these species now and in
the future. Rather, animals whose populations may decline as wetland habitats become
fragmented by development are of key concern. For example, breeding success of neotropical
migrant birds in fragmented forests of Illinois was extremely low due to high predation rates and
brood parasitism by brown-headed cowbirds (Robinson 1990). Newmark (1991) reported local
extinctions of forest interior birds in Tanzania due to fragmentation of tropical forests.
Fragmentation of wetlands is an important issue for wildlife managers to address. Some useful
references on fragmentation relative to forest birds are Askins et al. (1987), Robbins et al.
(1989), Freemark and Merriam (1986), and Freemark and Collins (1992). The latter study
includes a list of area-sensitive or forest interior birds for the eastern United States. The work of
Robbins et al. (1989) addressed area requirements of forest birds in the Mid-Atlantic states and
may be useful further south along the coastal plain. They found that species such as the black-throated
blue warbler, cerulean warbler, Canada warbler, and black-and-white warbler required
very large tracts of forest for breeding. Ground-nesters, such as veery, black-and-white warbler,
worm-eating warbler, ovenbird, waterthrushes, and Kentucky warbler, are particularly sensitive
to predation which may be increased in fragmented landscapes. Robbins et al. (1989) suggest a
minimum forest size of 7,410 acres to retain all species of the forest-breeding avifauna in the
Mid-Atlantic region. Schroeder (1996) noted that to conserve regional biodiversity, maintenance
of large-area habitats for forest interior birds is essential. As mentioned previously, Robbins et
al. (1989) suggest a minimum forest size of 7,410 acres to retain all species of the forest-breeding
avifauna in the Mid-Atlantic region. Consequently, forested areas 7,000 acres and
larger that contained contiguous palustrine forested wetlands and upland forests are important for
maintaining regional biodiversity of avifauna on the Atlantic Coastal Plain based on
recommendations by Robbins et al. (1989). Forested wetlands within large forest blocks 7,000
acres or more were rated as having potential for providing high value habitat for other wildlife.
21
While many amphibians are strictly aquatic animals living in water, salamanders, spring peepers,
and chorus frogs spend most of their adult lives in other wetlands and upland habitats, but use
open-water wetlands (including vernal pools) for breeding. For these species, small isolated
permanently flooded or semipermanently flooded wetlands (including ponds) in an upland forest
matrix (e.g., woodland vernal pools) have been rated as having high habitat value and other
wetlands contiguous to or within 100m of these wetlands have also been similarly rated.
Although this assessment focuses on wetlands, it is important to recognize that upland forests
adjacent to these breeding ponds are prime habitats for the juveniles and adults of these species.
Many terrestrial mammals make use of wetlands including rabbits, raccoons, and deer. For these
animals, large wetlands (> 20 acres) regardless of vegetative cover but excluding pine
plantations and smaller diverse wetlands (10-20 acres with multiple cover types) have been rated
as high value. Freshwater wetlands on or near back-barrier islands (including major hammocks)
are particularly valuable habitat for numerous island wildlife. Any remaining vegetated
wetlands are designated as having moderate value for providing wildlife habitat.
Please note that with the exception of vernal pools (woodland ponds), ponds are not listed as
important as significant for "other wildlife." Wildlife species living in ponds, such as several
species of frogs and turtles, are mentioned in the discussion of fish and aquatic invertebrate
habitat, since wetlands designated as important for fish and invertebrates provide required
habitat for these species.
High *Forested wetlands within 7000-acre blocks of forest, vegetated
wetlands >20 acres (excluding open water, nonvegetated areas, and
pine plantations), small diverse wetlands (10-20 acres with 2 or
more covertypes; excluding open water as one of the covertypes),
*small isolated permanently flooded or semipermanently flooded
wetlands within an upland forest matrix (including small ponds
that may be vernal pools) and contiguous wetlands, small vegetated
wetlands on or near coastal back-barrier islands (including those on
major hammocks)
Moderate Other vegetated wetlands
*Not identified for the coastal county project.
Given the general nature of this assessment of "other wildlife habitat," other individuals may
want to refine this assessment in the future by having biologists designate "target species" that
may be used to identify important wildlife habitats in a particular watershed. After doing this,
they could identify criteria that may be used to identify potentially significant habitat for these
species in the watershed.
22
Provision of Unique, Uncommon, or Highly Diverse Wetland Plant Communities
This function is used to identify wetlands that are unique or uncommon wetland types in a
watershed or other study area, or that represent highly diverse plant communities. All riverine
and palustrine tidal emergent and scrub-shrub wetlands (regularly flooded, seasonally flooded-tidal,
and semipermanently flooded-tidal) and estuarine oligohaline vegetated wetlands are
identified as significant for this function because they often possess some of the most diverse
wetland plant communities along the Atlantic Coast. While Phragmites-dominated wetlands are
generally excluded from this listing, any wetland supporting stands of the native species should
be recognized as a significant habitat. While this type was not mapped during the updated
inventory, it may be added from documented occurrences if desirable. Generally, however, the
use of Natural Heritage Program data and other data are beyond the scope of this remotely
sensed approach to wetland functional analysis. Consequently, wetlands designated as
potentially significant for this function by the W-PAWF assessment are simply a starting point
or, in other words, a foundation to build upon. Local knowledge of significant wetlands and
Natural Heritage Program data can be applied by others to further refine the list of wetlands
important for this function for specific geographic areas.
The following are examples of wetland types viewed as potentially significant for the provision
of habitat for unique or diverse wetland plant communities in coastal Georgia (Note: The ones
underlined were identified during the inventory):
Significant Estuarine oligohaline vegetated wetlands
Riverine tidal emergent wetlands (including tidal flats that are often
colonized by nonpersistent plants during the growing season)
Palustrine tidal emergent wetlands (regularly flooded, seasonally flooded
tidal, and semipermanently flooded-tidal water regimes)
Palustrine tidal scrub-shrub wetlands (regularly flooded, seasonally
flooded-tidal, and semipermanently flooded-tidal water regimes)
Freshwater vegetated wetlands on barrier islands (semipermanently
flooded, semipermanently flooded-tidal, and permanently flooded)
Brackish marshes at upper edge of salt marshes
Stands of native Phragmites (Note: These stands have not been identified
in the wetland mapping, but can be identified from our sources.)
Carolina bay wetlands (relatively intact)
Palustrine vegetated wetlands permanently flooded
.
23
Summary
The State of Georgia has added descriptors for landscape position, landform, and water flow path
to its updated wetland digital database for six coastal counties. When LLWW descriptors are
combined with typical NWI attributes from Cowardin et al. 1979 (system, subsystem, class,
subclass, water regime, and special modifiers), a NWIPlus database is created. It contains many
properties for each wetland that can be used to produce a preliminary landscape-level assessment
of wetland functions for large geographic areas. The subject report provides the rationale for the
criteria used to identify wetlands of potential significance for eleven functions. These functions
include: 1) surface water detention, 2) coastal storm surge detention, 3) streamflow maintenance,
4) nutrient transformation, 5) carbon sequestration, 6) sediment and other particulate retention,
7) bank and shoreline stabilization, 8) provision of fish and aquatic invertebrate habitat, 9)
provision of waterfowl and waterbird habitat, 10) provision of other wildlife habitat, and 11)
provision of habitat for unique, uncommon, or highly diverse wetland plant communities. The
preliminary nature of this type of functional assessment must be emphasized and while it
provides a valuable landscape-level perspective on wetland functions, field investigations are
required to refine these findings for specific wetlands or areas of interest.
24
Acknowledgments
The Georgia relationships between NWIPlus features and eleven functions were developed with
help from participants of the August 31, 2010 workshop at Little St. Simons Island. Jan
Mackinnon (GA DNR, Coastal Resources Division) was instrumental in organizing the
workshop. Workshop participants included: Chandra Franklin (Savannah State University),
Clark Alexander (Skidaway Institute of Oceanography), Dorset Hurley (Sapelo Island National
Estuarine Research Reserve), Dominic Guadagnoli (GA DNR), Gabe Gaddis (GA DNR), Deb
Barreiro (GA DNR), Karl Burgess (GA DNR), Jill Andrews (Georgia Coastal Management
Program), Bill Wikoff (U.S. Fish and Wildlife Service), Chris Capolla (U.S. Fish and Wildlife
Service), Ralph Tiner (U.S. Fish and Wildlife Service), Brandon Moody (GA DNR
Environmental Protection Agency), Brad Winn (GA DNR Wildife Resources Division), Shelly
Krueger (University of Georgia, Marine Extension Service), Amanda Wrona (The Nature
Conservancy), Kelly O’Rourke (Georgia Coastal Management Program), Sonny Emmert
(Georgia Coastal Management Program), Dale Caldwell (GA Environmental Protection
Division), Jeb Byers (University of Georgia, Odum School of Ecology), Risa Cohen (Georgia
Southern University), Katy Freas (U.S. Army Corps of Engineers), Rhonda Evans (U.S.
Environmental Protection Agency, Region IV), Tony Able (U.S. Environmental Protection
Agency, Region IV), John Hefner (Atkins North America, formerly PBS&J, Raleigh, NC), Dave
O’Loughlin (Atkins North America), Rainor Gresham (Atkins North America), Ben Cogdell
(Atkins North America), Keith Parsons (GA Environmental Protection Division), Steve Calver
(U.S. Army Corps of Engineers Planning Division), Susan Reeves (GA DNR), Jan Mackinnon,
and Scott Coleman (Little St. Simons Island).
The draft document was reviewed by personnel from Atkins North America and the GA DNR’s
Coastal Resources Division. Rainor Gresham provided a listing of the wetland types that were
mapped in the study area for each wetland function. This information was used to highlight
those wetlands in the listing of potential wetlands of significance for each function.
The foundation for the wetland characteristics-function relationships was laid over the past 15
years and many people had a hand in the process and were recognized in the 2003 correlation
report for the Northeast (Tiner 2003b). Since then additional peer review comments were
subsequently provided by Dr. Robert Brooks (Pennsylvania State University), Dr. Christopher
Cirmo (Cortland State University), Dr. Andrew Baldwin (University of Maryland), Dr. Mark
Brinson (East Carolina University), Dr. Donald Leopold (State University of New York-
Syracuse), Matt Schweisberg (U.S. EPA, Region 1), Dr. Charles Roman (U.S. Geological
Survey, University of Rhode Island), and Dr. Aram Calhoun (University of Maine). Their
comments were helpful in improving the document.
25
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